[role="xpack"]
[[security-api-saml-prepare-authentication]]
=== SAML prepare authentication API

Creates a SAML authentication request (`<AuthnRequest>`) as a URL string, based on the configuration of the respective SAML realm in {es}.

NOTE: This API is intended for use by custom web applications other than {kib}.
If you are using {kib}, see the <<saml-guide>>.

[[security-api-saml-prepare-authentication-request]]
==== {api-request-title}

`POST /_security/saml/prepare`

[[security-api-saml-prepare-authentication-desc]]
==== {api-description-title}

This API returns a URL pointing to the SAML Identity
Provider. You can use the URL to redirect the browser of the user in order to
continue the authentication process. The URL includes a single parameter named `SAMLRequest`,
which contains a SAML Authentication request that is deflated and
Base64 encoded. If the configuration dictates that SAML authentication requests
should be signed, the URL has two extra parameters named `SigAlg` and
`Signature`. These parameters contain the algorithm used for the signature and
the signature value itself.
It also returns a random string that uniquely identifies this SAML Authentication request. The
caller of this API needs to store this identifier as it needs to used in a following step of
the authentication process (see <<security-api-saml-authenticate,SAML authenticate API>>).

{es} exposes all the necessary SAML related functionality via the SAML APIs.
These APIs are used internally by {kib} in order to provide SAML based
authentication, but can also be used by other custom web applications or other
clients. See also <<security-api-saml-authenticate,SAML authenticate API>>,
<<security-api-saml-invalidate,SAML invalidate API>>, and
<<security-api-saml-logout,SAML logout API>>.

[[security-api-saml-prepare-authentication-request-body]]
==== {api-request-body-title}

`acs`::
  (Optional, string) The Assertion Consumer Service URL that matches the one of the SAML
  realms in {es}. The realm is used to generate the authentication request.
  You must specify either this parameter or the `realm` parameter.

`realm`::
  (Optional, string) The name of the SAML realm in {es} for which the configuration is
  used to generate the authentication request. You must specify either this parameter or the `acs`
  parameter.

[[security-api-saml-prepare-authentication-response-body]]
==== {api-response-body-title}  

`id`::
  (string) A unique identifier for the SAML Request to be stored by the caller
  of the API.

`realm`::
  (string) The name of the {es} realm that was used to construct the
  authentication request.

`redirect`::
  (string) The URL to redirect the user to.

[[security-api-saml-prepare-authentication-example]]
==== {api-examples-title}

The following example generates a SAML authentication request for the SAML realm with name `saml1`

[source,console]
--------------------------------------------------
POST /_security/saml/prepare
{
  "realm" : "saml1"
}
--------------------------------------------------

The following example generates a SAML authentication request for the SAML realm with an Assertion
Consuming Service URL matching `https://kibana.org/api/security/v1/saml

[source,console]
--------------------------------------------------
POST /_security/saml/prepare
{
  "acs" : "https://kibana.org/api/security/v1/saml"
}
--------------------------------------------------

This API returns the following response:

[source,js]
-------------------------------------------------
{
  "redirect": "https://my-idp.org/login?SAMLRequest=fVJdc6IwFP0rmbwDgUKLGbFDtc462%2B06FX3Yl50rBJsKCZsbrPbXL6J22hdfk%2FNx7zl3eL%2BvK7ITBqVWCfVdRolQuS6k2iR0mU2dmN6Phgh1FTQ8be2rehH%2FWoGWdESF%2FPST0NYorgElcgW1QG5zvkh%2FPfHAZbwx2upcV5SkiMLYzmqsFba1MAthdjIXy5enhL5a23DPOyo6W7kGBa7cwhZ2gO7G8OiW%2BR400kORt0bag7fzezAlk24eqcD2OxxlsNN5O3MdsW9c6CZnbq7rntF4d3s0D7BaHTZhIWN52P%2BcjiuGRbDU6cdj%2BEjJbJLQv4N4ADdhxBiEZbQuWclY4Q8iABbCXczCdSiKMAC%2FgyO2YqbQgrIJDZg%2FcFjsMD%2Fzb3gUcBa5sR%2F9oWR%2BzuJBqlPG14Jbn0DIf2TZ3Jn%2FXmSUrC5ddQB6bob37uZrJdeF4dIDHV3iuhb70Ptq83kOz53ubDLXlcwPJK0q%2FT42AqxIaAkVCkqm2tRgr49yfJGFU%2FZQ3hy3QyuUpd7obPv97kb%2FAQ%3D%3D"}",
  "realm": "saml1",
  "id": "_989a34500a4f5bf0f00d195aa04a7804b4ed42a1"
}
-------------------------------------------------
// NOTCONSOLE