66 lines
3.7 KiB
Plaintext
66 lines
3.7 KiB
Plaintext
[[runas]]
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= Run-As Authentication Replacement
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[[runas-overview]]
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The `AbstractSecurityInterceptor` is able to temporarily replace the `Authentication` object in the `SecurityContext` and `SecurityContextHolder` during the secure object callback phase.
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This only occurs if the original `Authentication` object was successfully processed by the `AuthenticationManager` and `AccessDecisionManager`.
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The `RunAsManager` indicates the replacement `Authentication` object, if any, that should be used during the `SecurityInterceptorCallback`.
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By temporarily replacing the `Authentication` object during the secure object callback phase, the secured invocation can call other objects that require different authentication and authorization credentials.
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It can also perform any internal security checks for specific `GrantedAuthority` objects.
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Because Spring Security provides a number of helper classes that automatically configure remoting protocols based on the contents of the `SecurityContextHolder`, these run-as replacements are particularly useful when calling remote web services.
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[[runas-config]]
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== Configuration
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Spring Security provices a `RunAsManager` interface:
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====
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[source,java]
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----
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Authentication buildRunAs(Authentication authentication, Object object,
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List<ConfigAttribute> config);
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boolean supports(ConfigAttribute attribute);
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boolean supports(Class clazz);
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----
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====
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The first method returns the `Authentication` object that should replace the existing `Authentication` object for the duration of the method invocation.
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If the method returns `null`, it indicates no replacement should be made.
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The second method is used by the `AbstractSecurityInterceptor` as part of its startup validation of configuration attributes.
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The `supports(Class)` method is called by a security interceptor implementation to ensure that the configured `RunAsManager` supports the type of secure object that the security interceptor presents.
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Spring Security provides one concrete implementation of `RunAsManager`.
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The `RunAsManagerImpl` class returns a replacement `RunAsUserToken` if any `ConfigAttribute` starts with `RUN_AS_`.
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If any such `ConfigAttribute` is found, the replacement `RunAsUserToken` contains the same principal, credentials, and granted authorities as the original `Authentication` object, along with a new `SimpleGrantedAuthority` for each `RUN_AS_` `ConfigAttribute`.
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Each new `SimpleGrantedAuthority` is prefixed with `ROLE_`, followed by the `RUN_AS` `ConfigAttribute`.
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For example, a `RUN_AS_SERVER` results in the replacement `RunAsUserToken` containing a `ROLE_RUN_AS_SERVER` granted authority.
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The replacement `RunAsUserToken` is like any other `Authentication` object.
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It needs to be authenticated by the `AuthenticationManager`, probably through delegation to a suitable `AuthenticationProvider`.
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The `RunAsImplAuthenticationProvider` performs such authentication.
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It accepts as valid any `RunAsUserToken` presented.
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To ensure malicious code does not create a `RunAsUserToken` and present it for guaranteed acceptance by the `RunAsImplAuthenticationProvider`, the hash of a key is stored in all generated tokens.
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The `RunAsManagerImpl` and `RunAsImplAuthenticationProvider` is created in the bean context with the same key:
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====
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[source,xml]
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----
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<bean id="runAsManager"
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class="org.springframework.security.access.intercept.RunAsManagerImpl">
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<property name="key" value="my_run_as_password"/>
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</bean>
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<bean id="runAsAuthenticationProvider"
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class="org.springframework.security.access.intercept.RunAsImplAuthenticationProvider">
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<property name="key" value="my_run_as_password"/>
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</bean>
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----
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====
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By using the same key, each `RunAsUserToken` can be validated because it was created by an approved `RunAsManagerImpl`.
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The `RunAsUserToken` is immutable after creation, for security reasons.
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