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= OAuth 2.0 Resource Server JWT
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[[webflux-oauth2resourceserver-jwt-minimaldependencies]]
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== Minimal Dependencies for JWT
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Most Resource Server support is collected into `spring-security-oauth2-resource-server`.
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However, the support for decoding and verifying JWTs is in `spring-security-oauth2-jose`, meaning that both are necessary in order to have a working resource server that supports JWT-encoded Bearer Tokens.
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[[webflux-oauth2resourceserver-jwt-minimalconfiguration]]
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== Minimal Configuration for JWTs
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When using https://spring.io/projects/spring-boot[Spring Boot], configuring an application as a resource server consists of two basic steps.
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First, include the needed dependencies and second, indicate the location of the authorization server.
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=== Specifying the Authorization Server
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In a Spring Boot application, to specify which authorization server to use, simply do:
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[source,yml]
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----
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spring:
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  security:
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    oauth2:
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      resourceserver:
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        jwt:
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          issuer-uri: https://idp.example.com/issuer
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----
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Where `https://idp.example.com/issuer` is the value contained in the `iss` claim for JWT tokens that the authorization server will issue.
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Resource Server will use this property to further self-configure, discover the authorization server's public keys, and subsequently validate incoming JWTs.
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[NOTE]
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To use the `issuer-uri` property, it must also be true that one of `https://idp.example.com/issuer/.well-known/openid-configuration`, `https://idp.example.com/.well-known/openid-configuration/issuer`, or `https://idp.example.com/.well-known/oauth-authorization-server/issuer` is a supported endpoint for the authorization server.
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This endpoint is referred to as a https://openid.net/specs/openid-connect-discovery-1_0.html#ProviderConfig[Provider Configuration] endpoint or a https://tools.ietf.org/html/rfc8414#section-3[Authorization Server Metadata] endpoint.
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And that's it!
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=== Startup Expectations
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When this property and these dependencies are used, Resource Server will automatically configure itself to validate JWT-encoded Bearer Tokens.
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It achieves this through a deterministic startup process:
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1. Hit the Provider Configuration or Authorization Server Metadata endpoint, processing the response for the `jwks_url` property
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2. Configure the validation strategy to query `jwks_url` for valid public keys
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3. Configure the validation strategy to validate each JWTs `iss` claim against `https://idp.example.com`.
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A consequence of this process is that the authorization server must be up and receiving requests in order for Resource Server to successfully start up.
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[NOTE]
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If the authorization server is down when Resource Server queries it (given appropriate timeouts), then startup will fail.
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=== Runtime Expectations
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Once the application is started up, Resource Server will attempt to process any request containing an `Authorization: Bearer` header:
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[source,html]
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----
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GET / HTTP/1.1
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Authorization: Bearer some-token-value # Resource Server will process this
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----
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So long as this scheme is indicated, Resource Server will attempt to process the request according to the Bearer Token specification.
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Given a well-formed JWT, Resource Server will:
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1. Validate its signature against a public key obtained from the `jwks_url` endpoint during startup and matched against the JWTs header
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2. Validate the JWTs `exp` and `nbf` timestamps and the JWTs `iss` claim, and
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3. Map each scope to an authority with the prefix `SCOPE_`.
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[NOTE]
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As the authorization server makes available new keys, Spring Security will automatically rotate the keys used to validate the JWT tokens.
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The resulting `Authentication#getPrincipal`, by default, is a Spring Security `Jwt` object, and `Authentication#getName` maps to the JWT's `sub` property, if one is present.
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From here, consider jumping to:
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<<webflux-oauth2resourceserver-jwt-jwkseturi,How to Configure without Tying Resource Server startup to an authorization server's availability>>
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<<webflux-oauth2resourceserver-jwt-sansboot,How to Configure without Spring Boot>>
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[[webflux-oauth2resourceserver-jwt-jwkseturi]]
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=== Specifying the Authorization Server JWK Set Uri Directly
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If the authorization server doesn't support any configuration endpoints, or if Resource Server must be able to start up independently from the authorization server, then the `jwk-set-uri` can be supplied as well:
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[source,yaml]
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----
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spring:
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  security:
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    oauth2:
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      resourceserver:
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        jwt:
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          issuer-uri: https://idp.example.com
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          jwk-set-uri: https://idp.example.com/.well-known/jwks.json
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----
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[NOTE]
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The JWK Set uri is not standardized, but can typically be found in the authorization server's documentation
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Consequently, Resource Server will not ping the authorization server at startup.
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We still specify the `issuer-uri` so that Resource Server still validates the `iss` claim on incoming JWTs.
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[NOTE]
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This property can also be supplied directly on the <<webflux-oauth2resourceserver-jwt-jwkseturi-dsl,DSL>>.
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[[webflux-oauth2resourceserver-jwt-sansboot]]
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=== Overriding or Replacing Boot Auto Configuration
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There are two ``@Bean``s that Spring Boot generates on Resource Server's behalf.
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The first is a `SecurityWebFilterChain` that configures the app as a resource server. When including `spring-security-oauth2-jose`, this `SecurityWebFilterChain` looks like:
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.Resource Server SecurityWebFilterChain
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====
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.Java
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[source,java,role="primary"]
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----
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@Bean
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SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
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	http
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		.authorizeExchange(exchanges -> exchanges
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			.anyExchange().authenticated()
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		)
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		.oauth2ResourceServer(OAuth2ResourceServerSpec::jwt)
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	return http.build();
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}
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----
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.Kotlin
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[source,kotlin,role="secondary"]
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----
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@Bean
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fun springSecurityFilterChain(http: ServerHttpSecurity): SecurityWebFilterChain {
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    return http {
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        authorizeExchange {
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            authorize(anyExchange, authenticated)
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        }
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        oauth2ResourceServer {
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            jwt { }
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        }
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    }
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}
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----
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====
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If the application doesn't expose a `SecurityWebFilterChain` bean, then Spring Boot will expose the above default one.
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Replacing this is as simple as exposing the bean within the application:
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.Replacing SecurityWebFilterChain
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====
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.Java
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[source,java,role="primary"]
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----
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@Bean
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SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
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	http
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		.authorizeExchange(exchanges -> exchanges
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			.pathMatchers("/message/**").hasAuthority("SCOPE_message:read")
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			.anyExchange().authenticated()
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		)
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		.oauth2ResourceServer(oauth2 -> oauth2
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			.jwt(withDefaults())
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		);
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	return http.build();
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}
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----
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.Kotlin
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[source,kotlin,role="secondary"]
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----
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@Bean
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fun springSecurityFilterChain(http: ServerHttpSecurity): SecurityWebFilterChain {
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    return http {
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        authorizeExchange {
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            authorize("/message/**", hasAuthority("SCOPE_message:read"))
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            authorize(anyExchange, authenticated)
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        }
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        oauth2ResourceServer {
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            jwt { }
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        }
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    }
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}
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----
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====
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The above requires the scope of `message:read` for any URL that starts with `/messages/`.
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Methods on the `oauth2ResourceServer` DSL will also override or replace auto configuration.
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For example, the second `@Bean` Spring Boot creates is a `ReactiveJwtDecoder`, which decodes `String` tokens into validated instances of `Jwt`:
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.ReactiveJwtDecoder
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====
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.Java
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[source,java,role="primary"]
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----
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@Bean
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public ReactiveJwtDecoder jwtDecoder() {
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    return ReactiveJwtDecoders.fromIssuerLocation(issuerUri);
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}
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----
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.Kotlin
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[source,kotlin,role="secondary"]
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----
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@Bean
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fun jwtDecoder(): ReactiveJwtDecoder {
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    return ReactiveJwtDecoders.fromIssuerLocation(issuerUri)
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}
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----
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====
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[NOTE]
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Calling `{security-api-url}org/springframework/security/oauth2/jwt/ReactiveJwtDecoders.html#fromIssuerLocation-java.lang.String-[ReactiveJwtDecoders#fromIssuerLocation]` is what invokes the Provider Configuration or Authorization Server Metadata endpoint in order to derive the JWK Set Uri.
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If the application doesn't expose a `ReactiveJwtDecoder` bean, then Spring Boot will expose the above default one.
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And its configuration can be overridden using `jwkSetUri()` or replaced using `decoder()`.
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[[webflux-oauth2resourceserver-jwt-jwkseturi-dsl]]
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==== Using `jwkSetUri()`
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An authorization server's JWK Set Uri can be configured <<webflux-oauth2resourceserver-jwt-jwkseturi,as a configuration property>> or it can be supplied in the DSL:
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====
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.Java
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[source,java,role="primary"]
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----
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@Bean
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SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
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	http
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		.authorizeExchange(exchanges -> exchanges
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			.anyExchange().authenticated()
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		)
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		.oauth2ResourceServer(oauth2 -> oauth2
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			.jwt(jwt -> jwt
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				.jwkSetUri("https://idp.example.com/.well-known/jwks.json")
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			)
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		);
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	return http.build();
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}
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----
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.Kotlin
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[source,kotlin,role="secondary"]
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----
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@Bean
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fun springSecurityFilterChain(http: ServerHttpSecurity): SecurityWebFilterChain {
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    return http {
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        authorizeExchange {
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            authorize(anyExchange, authenticated)
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        }
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        oauth2ResourceServer {
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            jwt {
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                jwkSetUri = "https://idp.example.com/.well-known/jwks.json"
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            }
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        }
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    }
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}
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----
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====
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Using `jwkSetUri()` takes precedence over any configuration property.
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[[webflux-oauth2resourceserver-jwt-decoder-dsl]]
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==== Using `decoder()`
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More powerful than `jwkSetUri()` is `decoder()`, which will completely replace any Boot auto configuration of `JwtDecoder`:
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====
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.Java
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[source,java,role="primary"]
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----
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@Bean
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SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
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	http
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		.authorizeExchange(exchanges -> exchanges
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			.anyExchange().authenticated()
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		)
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		.oauth2ResourceServer(oauth2 -> oauth2
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			.jwt(jwt -> jwt
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				.decoder(myCustomDecoder())
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			)
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		);
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    return http.build();
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}
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----
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.Kotlin
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[source,kotlin,role="secondary"]
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----
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@Bean
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fun springSecurityFilterChain(http: ServerHttpSecurity): SecurityWebFilterChain {
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    return http {
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        authorizeExchange {
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            authorize(anyExchange, authenticated)
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        }
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        oauth2ResourceServer {
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            jwt {
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                jwtDecoder = myCustomDecoder()
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            }
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        }
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    }
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}
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----
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====
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This is handy when deeper configuration, like <<webflux-oauth2resourceserver-jwt-validation,validation>>, is necessary.
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[[webflux-oauth2resourceserver-decoder-bean]]
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==== Exposing a `ReactiveJwtDecoder` `@Bean`
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Or, exposing a `ReactiveJwtDecoder` `@Bean` has the same effect as `decoder()`:
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====
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.Java
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[source,java,role="primary"]
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----
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@Bean
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public ReactiveJwtDecoder jwtDecoder() {
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    return NimbusReactiveJwtDecoder.withJwkSetUri(jwkSetUri).build();
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}
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----
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.Kotlin
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[source,kotlin,role="secondary"]
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----
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@Bean
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fun jwtDecoder(): ReactiveJwtDecoder {
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    return ReactiveJwtDecoders.fromIssuerLocation(issuerUri)
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}
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----
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====
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[[webflux-oauth2resourceserver-jwt-decoder-algorithm]]
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== Configuring Trusted Algorithms
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By default, `NimbusReactiveJwtDecoder`, and hence Resource Server, will only trust and verify tokens using `RS256`.
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You can customize this via <<webflux-oauth2resourceserver-jwt-boot-algorithm,Spring Boot>> or <<webflux-oauth2resourceserver-jwt-decoder-builder,the NimbusJwtDecoder builder>>.
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[[webflux-oauth2resourceserver-jwt-boot-algorithm]]
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=== Via Spring Boot
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The simplest way to set the algorithm is as a property:
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[source,yaml]
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----
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spring:
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  security:
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    oauth2:
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      resourceserver:
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        jwt:
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          jws-algorithm: RS512
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          jwk-set-uri: https://idp.example.org/.well-known/jwks.json
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----
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[[webflux-oauth2resourceserver-jwt-decoder-builder]]
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=== Using a Builder
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For greater power, though, we can use a builder that ships with `NimbusReactiveJwtDecoder`:
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====
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.Java
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[source,java,role="primary"]
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----
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@Bean
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ReactiveJwtDecoder jwtDecoder() {
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    return NimbusReactiveJwtDecoder.withJwkSetUri(this.jwkSetUri)
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            .jwsAlgorithm(RS512).build();
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}
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----
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.Kotlin
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[source,kotlin,role="secondary"]
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----
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@Bean
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fun jwtDecoder(): ReactiveJwtDecoder {
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    return NimbusReactiveJwtDecoder.withJwkSetUri(this.jwkSetUri)
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            .jwsAlgorithm(RS512).build()
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}
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----
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====
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Calling `jwsAlgorithm` more than once will configure `NimbusReactiveJwtDecoder` to trust more than one algorithm, like so:
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====
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.Java
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[source,java,role="primary"]
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----
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@Bean
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ReactiveJwtDecoder jwtDecoder() {
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    return NimbusReactiveJwtDecoder.withJwkSetUri(this.jwkSetUri)
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            .jwsAlgorithm(RS512).jwsAlgorithm(ES512).build();
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}
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----
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.Kotlin
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[source,kotlin,role="secondary"]
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----
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@Bean
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fun jwtDecoder(): ReactiveJwtDecoder {
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    return NimbusReactiveJwtDecoder.withJwkSetUri(this.jwkSetUri)
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            .jwsAlgorithm(RS512).jwsAlgorithm(ES512).build()
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}
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----
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====
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Or, you can call `jwsAlgorithms`:
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====
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.Java
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[source,java,role="primary"]
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----
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@Bean
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ReactiveJwtDecoder jwtDecoder() {
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    return NimbusReactiveJwtDecoder.withJwkSetUri(this.jwkSetUri)
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            .jwsAlgorithms(algorithms -> {
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                    algorithms.add(RS512);
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                    algorithms.add(ES512);
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						|
            }).build();
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}
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						|
----
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						|
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.Kotlin
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[source,kotlin,role="secondary"]
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----
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@Bean
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fun jwtDecoder(): ReactiveJwtDecoder {
 | 
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    return NimbusReactiveJwtDecoder.withJwkSetUri(this.jwkSetUri)
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            .jwsAlgorithms {
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                it.add(RS512)
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                it.add(ES512)
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            }
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            .build()
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}
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----
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====
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[[webflux-oauth2resourceserver-jwt-decoder-public-key]]
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=== Trusting a Single Asymmetric Key
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						|
 | 
						|
Simpler than backing a Resource Server with a JWK Set endpoint is to hard-code an RSA public key.
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The public key can be provided via <<webflux-oauth2resourceserver-jwt-decoder-public-key-boot,Spring Boot>> or by <<webflux-oauth2resourceserver-jwt-decoder-public-key-builder,Using a Builder>>.
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[[webflux-oauth2resourceserver-jwt-decoder-public-key-boot]]
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==== Via Spring Boot
 | 
						|
 | 
						|
Specifying a key via Spring Boot is quite simple.
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						|
The key's location can be specified like so:
 | 
						|
 | 
						|
[source,yaml]
 | 
						|
----
 | 
						|
spring:
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						|
  security:
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						|
    oauth2:
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						|
      resourceserver:
 | 
						|
        jwt:
 | 
						|
          public-key-location: classpath:my-key.pub
 | 
						|
----
 | 
						|
 | 
						|
Or, to allow for a more sophisticated lookup, you can post-process the `RsaKeyConversionServicePostProcessor`:
 | 
						|
 | 
						|
.BeanFactoryPostProcessor
 | 
						|
====
 | 
						|
.Java
 | 
						|
[source,java,role="primary"]
 | 
						|
----
 | 
						|
@Bean
 | 
						|
BeanFactoryPostProcessor conversionServiceCustomizer() {
 | 
						|
    return beanFactory ->
 | 
						|
        beanFactory.getBean(RsaKeyConversionServicePostProcessor.class)
 | 
						|
                .setResourceLoader(new CustomResourceLoader());
 | 
						|
}
 | 
						|
----
 | 
						|
 | 
						|
.Kotlin
 | 
						|
[source,kotlin,role="secondary"]
 | 
						|
----
 | 
						|
@Bean
 | 
						|
fun conversionServiceCustomizer(): BeanFactoryPostProcessor {
 | 
						|
    return BeanFactoryPostProcessor { beanFactory: ConfigurableListableBeanFactory ->
 | 
						|
        beanFactory.getBean<RsaKeyConversionServicePostProcessor>()
 | 
						|
                .setResourceLoader(CustomResourceLoader())
 | 
						|
    }
 | 
						|
}
 | 
						|
----
 | 
						|
====
 | 
						|
 | 
						|
Specify your key's location:
 | 
						|
 | 
						|
[source,yaml]
 | 
						|
----
 | 
						|
key.location: hfds://my-key.pub
 | 
						|
----
 | 
						|
 | 
						|
And then autowire the value:
 | 
						|
 | 
						|
====
 | 
						|
.Java
 | 
						|
[source,java,role="primary"]
 | 
						|
----
 | 
						|
@Value("${key.location}")
 | 
						|
RSAPublicKey key;
 | 
						|
----
 | 
						|
 | 
						|
.Kotlin
 | 
						|
[source,kotlin,role="secondary"]
 | 
						|
----
 | 
						|
@Value("\${key.location}")
 | 
						|
val key: RSAPublicKey? = null
 | 
						|
----
 | 
						|
====
 | 
						|
 | 
						|
[[webflux-oauth2resourceserver-jwt-decoder-public-key-builder]]
 | 
						|
==== Using a Builder
 | 
						|
 | 
						|
To wire an `RSAPublicKey` directly, you can simply use the appropriate `NimbusReactiveJwtDecoder` builder, like so:
 | 
						|
 | 
						|
====
 | 
						|
.Java
 | 
						|
[source,java,role="primary"]
 | 
						|
----
 | 
						|
@Bean
 | 
						|
public ReactiveJwtDecoder jwtDecoder() {
 | 
						|
    return NimbusReactiveJwtDecoder.withPublicKey(this.key).build();
 | 
						|
}
 | 
						|
----
 | 
						|
 | 
						|
.Kotlin
 | 
						|
[source,kotlin,role="secondary"]
 | 
						|
----
 | 
						|
@Bean
 | 
						|
fun jwtDecoder(): ReactiveJwtDecoder {
 | 
						|
    return NimbusReactiveJwtDecoder.withPublicKey(key).build()
 | 
						|
}
 | 
						|
----
 | 
						|
====
 | 
						|
 | 
						|
[[webflux-oauth2resourceserver-jwt-decoder-secret-key]]
 | 
						|
=== Trusting a Single Symmetric Key
 | 
						|
 | 
						|
Using a single symmetric key is also simple.
 | 
						|
You can simply load in your `SecretKey` and use the appropriate `NimbusReactiveJwtDecoder` builder, like so:
 | 
						|
 | 
						|
====
 | 
						|
.Java
 | 
						|
[source,java,role="primary"]
 | 
						|
----
 | 
						|
@Bean
 | 
						|
public ReactiveJwtDecoder jwtDecoder() {
 | 
						|
    return NimbusReactiveJwtDecoder.withSecretKey(this.key).build();
 | 
						|
}
 | 
						|
----
 | 
						|
 | 
						|
.Kotlin
 | 
						|
[source,kotlin,role="secondary"]
 | 
						|
----
 | 
						|
@Bean
 | 
						|
fun jwtDecoder(): ReactiveJwtDecoder {
 | 
						|
    return NimbusReactiveJwtDecoder.withSecretKey(this.key).build()
 | 
						|
}
 | 
						|
----
 | 
						|
====
 | 
						|
 | 
						|
[[webflux-oauth2resourceserver-jwt-authorization]]
 | 
						|
=== Configuring Authorization
 | 
						|
 | 
						|
A JWT that is issued from an OAuth 2.0 Authorization Server will typically either have a `scope` or `scp` attribute, indicating the scopes (or authorities) it's been granted, for example:
 | 
						|
 | 
						|
`{ ..., "scope" : "messages contacts"}`
 | 
						|
 | 
						|
When this is the case, Resource Server will attempt to coerce these scopes into a list of granted authorities, prefixing each scope with the string "SCOPE_".
 | 
						|
 | 
						|
This means that to protect an endpoint or method with a scope derived from a JWT, the corresponding expressions should include this prefix:
 | 
						|
 | 
						|
====
 | 
						|
.Java
 | 
						|
[source,java,role="primary"]
 | 
						|
----
 | 
						|
@Bean
 | 
						|
SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
 | 
						|
	http
 | 
						|
		.authorizeExchange(exchanges -> exchanges
 | 
						|
			.mvcMatchers("/contacts/**").hasAuthority("SCOPE_contacts")
 | 
						|
			.mvcMatchers("/messages/**").hasAuthority("SCOPE_messages")
 | 
						|
			.anyExchange().authenticated()
 | 
						|
		)
 | 
						|
		.oauth2ResourceServer(OAuth2ResourceServerSpec::jwt);
 | 
						|
    return http.build();
 | 
						|
}
 | 
						|
----
 | 
						|
 | 
						|
.Kotlin
 | 
						|
[source,kotlin,role="secondary"]
 | 
						|
----
 | 
						|
@Bean
 | 
						|
fun springSecurityFilterChain(http: ServerHttpSecurity): SecurityWebFilterChain {
 | 
						|
    return http {
 | 
						|
        authorizeExchange {
 | 
						|
            authorize("/contacts/**", hasAuthority("SCOPE_contacts"))
 | 
						|
            authorize("/messages/**", hasAuthority("SCOPE_messages"))
 | 
						|
            authorize(anyExchange, authenticated)
 | 
						|
        }
 | 
						|
        oauth2ResourceServer {
 | 
						|
            jwt { }
 | 
						|
        }
 | 
						|
    }
 | 
						|
}
 | 
						|
----
 | 
						|
====
 | 
						|
 | 
						|
Or similarly with method security:
 | 
						|
 | 
						|
====
 | 
						|
.Java
 | 
						|
[source,java,role="primary"]
 | 
						|
----
 | 
						|
@PreAuthorize("hasAuthority('SCOPE_messages')")
 | 
						|
public Flux<Message> getMessages(...) {}
 | 
						|
----
 | 
						|
 | 
						|
.Kotlin
 | 
						|
[source,kotlin,role="secondary"]
 | 
						|
----
 | 
						|
@PreAuthorize("hasAuthority('SCOPE_messages')")
 | 
						|
fun getMessages(): Flux<Message> { }
 | 
						|
----
 | 
						|
====
 | 
						|
 | 
						|
[[webflux-oauth2resourceserver-jwt-authorization-extraction]]
 | 
						|
==== Extracting Authorities Manually
 | 
						|
 | 
						|
However, there are a number of circumstances where this default is insufficient.
 | 
						|
For example, some authorization servers don't use the `scope` attribute, but instead have their own custom attribute.
 | 
						|
Or, at other times, the resource server may need to adapt the attribute or a composition of attributes into internalized authorities.
 | 
						|
 | 
						|
To this end, the DSL exposes `jwtAuthenticationConverter()`:
 | 
						|
 | 
						|
====
 | 
						|
.Java
 | 
						|
[source,java,role="primary"]
 | 
						|
----
 | 
						|
@Bean
 | 
						|
SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
 | 
						|
	http
 | 
						|
		.authorizeExchange(exchanges -> exchanges
 | 
						|
			.anyExchange().authenticated()
 | 
						|
		)
 | 
						|
		.oauth2ResourceServer(oauth2 -> oauth2
 | 
						|
			.jwt(jwt -> jwt
 | 
						|
				.jwtAuthenticationConverter(grantedAuthoritiesExtractor())
 | 
						|
			)
 | 
						|
		);
 | 
						|
	return http.build();
 | 
						|
}
 | 
						|
 | 
						|
Converter<Jwt, Mono<AbstractAuthenticationToken>> grantedAuthoritiesExtractor() {
 | 
						|
    JwtAuthenticationConverter jwtAuthenticationConverter =
 | 
						|
            new JwtAuthenticationConverter();
 | 
						|
    jwtAuthenticationConverter.setJwtGrantedAuthoritiesConverter
 | 
						|
            (new GrantedAuthoritiesExtractor());
 | 
						|
    return new ReactiveJwtAuthenticationConverterAdapter(jwtAuthenticationConverter);
 | 
						|
}
 | 
						|
----
 | 
						|
 | 
						|
.Kotlin
 | 
						|
[source,kotlin,role="secondary"]
 | 
						|
----
 | 
						|
@Bean
 | 
						|
fun springSecurityFilterChain(http: ServerHttpSecurity): SecurityWebFilterChain {
 | 
						|
    return http {
 | 
						|
        authorizeExchange {
 | 
						|
            authorize(anyExchange, authenticated)
 | 
						|
        }
 | 
						|
        oauth2ResourceServer {
 | 
						|
            jwt {
 | 
						|
                jwtAuthenticationConverter = grantedAuthoritiesExtractor()
 | 
						|
            }
 | 
						|
        }
 | 
						|
    }
 | 
						|
}
 | 
						|
 | 
						|
fun grantedAuthoritiesExtractor(): Converter<Jwt, Mono<AbstractAuthenticationToken>> {
 | 
						|
    val jwtAuthenticationConverter = JwtAuthenticationConverter()
 | 
						|
    jwtAuthenticationConverter.setJwtGrantedAuthoritiesConverter(GrantedAuthoritiesExtractor())
 | 
						|
    return ReactiveJwtAuthenticationConverterAdapter(jwtAuthenticationConverter)
 | 
						|
}
 | 
						|
----
 | 
						|
====
 | 
						|
 | 
						|
which is responsible for converting a `Jwt` into an `Authentication`.
 | 
						|
As part of its configuration, we can supply a subsidiary converter to go from `Jwt` to a `Collection` of granted authorities.
 | 
						|
 | 
						|
That final converter might be something like `GrantedAuthoritiesExtractor` below:
 | 
						|
 | 
						|
====
 | 
						|
.Java
 | 
						|
[source,java,role="primary"]
 | 
						|
----
 | 
						|
static class GrantedAuthoritiesExtractor
 | 
						|
        implements Converter<Jwt, Collection<GrantedAuthority>> {
 | 
						|
 | 
						|
    public Collection<GrantedAuthority> convert(Jwt jwt) {
 | 
						|
        Collection<?> authorities = (Collection<?>)
 | 
						|
                jwt.getClaims().getOrDefault("mycustomclaim", Collections.emptyList());
 | 
						|
 | 
						|
        return authorities.stream()
 | 
						|
                .map(Object::toString)
 | 
						|
                .map(SimpleGrantedAuthority::new)
 | 
						|
                .collect(Collectors.toList());
 | 
						|
    }
 | 
						|
}
 | 
						|
----
 | 
						|
 | 
						|
.Kotlin
 | 
						|
[source,kotlin,role="secondary"]
 | 
						|
----
 | 
						|
internal class GrantedAuthoritiesExtractor : Converter<Jwt, Collection<GrantedAuthority>> {
 | 
						|
    override fun convert(jwt: Jwt): Collection<GrantedAuthority> {
 | 
						|
        val authorities: List<Any> = jwt.claims
 | 
						|
                .getOrDefault("mycustomclaim", emptyList<Any>()) as List<Any>
 | 
						|
        return authorities
 | 
						|
                .map { it.toString() }
 | 
						|
                .map { SimpleGrantedAuthority(it) }
 | 
						|
    }
 | 
						|
}
 | 
						|
----
 | 
						|
====
 | 
						|
 | 
						|
For more flexibility, the DSL supports entirely replacing the converter with any class that implements `Converter<Jwt, Mono<AbstractAuthenticationToken>>`:
 | 
						|
 | 
						|
====
 | 
						|
.Java
 | 
						|
[source,java,role="primary"]
 | 
						|
----
 | 
						|
static class CustomAuthenticationConverter implements Converter<Jwt, Mono<AbstractAuthenticationToken>> {
 | 
						|
    public AbstractAuthenticationToken convert(Jwt jwt) {
 | 
						|
        return Mono.just(jwt).map(this::doConversion);
 | 
						|
    }
 | 
						|
}
 | 
						|
----
 | 
						|
 | 
						|
.Kotlin
 | 
						|
[source,kotlin,role="secondary"]
 | 
						|
----
 | 
						|
internal class CustomAuthenticationConverter : Converter<Jwt, Mono<AbstractAuthenticationToken>> {
 | 
						|
    override fun convert(jwt: Jwt): Mono<AbstractAuthenticationToken> {
 | 
						|
        return Mono.just(jwt).map(this::doConversion)
 | 
						|
    }
 | 
						|
}
 | 
						|
----
 | 
						|
====
 | 
						|
 | 
						|
[[webflux-oauth2resourceserver-jwt-validation]]
 | 
						|
=== Configuring Validation
 | 
						|
 | 
						|
Using <<webflux-oauth2resourceserver-jwt-minimalconfiguration,minimal Spring Boot configuration>>, indicating the authorization server's issuer uri, Resource Server will default to verifying the `iss` claim as well as the `exp` and `nbf` timestamp claims.
 | 
						|
 | 
						|
In circumstances where validation needs to be customized, Resource Server ships with two standard validators and also accepts custom `OAuth2TokenValidator` instances.
 | 
						|
 | 
						|
[[webflux-oauth2resourceserver-jwt-validation-clockskew]]
 | 
						|
==== Customizing Timestamp Validation
 | 
						|
 | 
						|
JWT's typically have a window of validity, with the start of the window indicated in the `nbf` claim and the end indicated in the `exp` claim.
 | 
						|
 | 
						|
However, every server can experience clock drift, which can cause tokens to appear expired to one server, but not to another.
 | 
						|
This can cause some implementation heartburn as the number of collaborating servers increases in a distributed system.
 | 
						|
 | 
						|
Resource Server uses `JwtTimestampValidator` to verify a token's validity window, and it can be configured with a `clockSkew` to alleviate the above problem:
 | 
						|
 | 
						|
====
 | 
						|
.Java
 | 
						|
[source,java,role="primary"]
 | 
						|
----
 | 
						|
@Bean
 | 
						|
ReactiveJwtDecoder jwtDecoder() {
 | 
						|
     NimbusReactiveJwtDecoder jwtDecoder = (NimbusReactiveJwtDecoder)
 | 
						|
             ReactiveJwtDecoders.fromIssuerLocation(issuerUri);
 | 
						|
 | 
						|
     OAuth2TokenValidator<Jwt> withClockSkew = new DelegatingOAuth2TokenValidator<>(
 | 
						|
            new JwtTimestampValidator(Duration.ofSeconds(60)),
 | 
						|
            new IssuerValidator(issuerUri));
 | 
						|
 | 
						|
     jwtDecoder.setJwtValidator(withClockSkew);
 | 
						|
 | 
						|
     return jwtDecoder;
 | 
						|
}
 | 
						|
----
 | 
						|
 | 
						|
.Kotlin
 | 
						|
[source,kotlin,role="secondary"]
 | 
						|
----
 | 
						|
@Bean
 | 
						|
fun jwtDecoder(): ReactiveJwtDecoder {
 | 
						|
    val jwtDecoder = ReactiveJwtDecoders.fromIssuerLocation(issuerUri) as NimbusReactiveJwtDecoder
 | 
						|
    val withClockSkew: OAuth2TokenValidator<Jwt> = DelegatingOAuth2TokenValidator(
 | 
						|
            JwtTimestampValidator(Duration.ofSeconds(60)),
 | 
						|
            JwtIssuerValidator(issuerUri))
 | 
						|
    jwtDecoder.setJwtValidator(withClockSkew)
 | 
						|
    return jwtDecoder
 | 
						|
}
 | 
						|
----
 | 
						|
====
 | 
						|
 | 
						|
[NOTE]
 | 
						|
By default, Resource Server configures a clock skew of 60 seconds.
 | 
						|
 | 
						|
[[webflux-oauth2resourceserver-validation-custom]]
 | 
						|
==== Configuring a Custom Validator
 | 
						|
 | 
						|
Adding a check for the `aud` claim is simple with the `OAuth2TokenValidator` API:
 | 
						|
 | 
						|
====
 | 
						|
.Java
 | 
						|
[source,java,role="primary"]
 | 
						|
----
 | 
						|
public class AudienceValidator implements OAuth2TokenValidator<Jwt> {
 | 
						|
    OAuth2Error error = new OAuth2Error("invalid_token", "The required audience is missing", null);
 | 
						|
 | 
						|
    public OAuth2TokenValidatorResult validate(Jwt jwt) {
 | 
						|
        if (jwt.getAudience().contains("messaging")) {
 | 
						|
            return OAuth2TokenValidatorResult.success();
 | 
						|
        } else {
 | 
						|
            return OAuth2TokenValidatorResult.failure(error);
 | 
						|
        }
 | 
						|
    }
 | 
						|
}
 | 
						|
----
 | 
						|
 | 
						|
.Kotlin
 | 
						|
[source,kotlin,role="secondary"]
 | 
						|
----
 | 
						|
class AudienceValidator : OAuth2TokenValidator<Jwt> {
 | 
						|
    var error: OAuth2Error = OAuth2Error("invalid_token", "The required audience is missing", null)
 | 
						|
    override fun validate(jwt: Jwt): OAuth2TokenValidatorResult {
 | 
						|
        return if (jwt.audience.contains("messaging")) {
 | 
						|
            OAuth2TokenValidatorResult.success()
 | 
						|
        } else {
 | 
						|
            OAuth2TokenValidatorResult.failure(error)
 | 
						|
        }
 | 
						|
    }
 | 
						|
}
 | 
						|
----
 | 
						|
====
 | 
						|
 | 
						|
Then, to add into a resource server, it's a matter of specifying the `ReactiveJwtDecoder` instance:
 | 
						|
 | 
						|
====
 | 
						|
.Java
 | 
						|
[source,java,role="primary"]
 | 
						|
----
 | 
						|
@Bean
 | 
						|
ReactiveJwtDecoder jwtDecoder() {
 | 
						|
    NimbusReactiveJwtDecoder jwtDecoder = (NimbusReactiveJwtDecoder)
 | 
						|
            ReactiveJwtDecoders.fromIssuerLocation(issuerUri);
 | 
						|
 | 
						|
    OAuth2TokenValidator<Jwt> audienceValidator = new AudienceValidator();
 | 
						|
    OAuth2TokenValidator<Jwt> withIssuer = JwtValidators.createDefaultWithIssuer(issuerUri);
 | 
						|
    OAuth2TokenValidator<Jwt> withAudience = new DelegatingOAuth2TokenValidator<>(withIssuer, audienceValidator);
 | 
						|
 | 
						|
    jwtDecoder.setJwtValidator(withAudience);
 | 
						|
 | 
						|
    return jwtDecoder;
 | 
						|
}
 | 
						|
----
 | 
						|
 | 
						|
.Kotlin
 | 
						|
[source,kotlin,role="secondary"]
 | 
						|
----
 | 
						|
@Bean
 | 
						|
fun jwtDecoder(): ReactiveJwtDecoder {
 | 
						|
    val jwtDecoder = ReactiveJwtDecoders.fromIssuerLocation(issuerUri) as NimbusReactiveJwtDecoder
 | 
						|
    val audienceValidator: OAuth2TokenValidator<Jwt> = AudienceValidator()
 | 
						|
    val withIssuer: OAuth2TokenValidator<Jwt> = JwtValidators.createDefaultWithIssuer(issuerUri)
 | 
						|
    val withAudience: OAuth2TokenValidator<Jwt> = DelegatingOAuth2TokenValidator(withIssuer, audienceValidator)
 | 
						|
    jwtDecoder.setJwtValidator(withAudience)
 | 
						|
    return jwtDecoder
 | 
						|
}
 | 
						|
----
 | 
						|
====
 |