Adds realm name OIDC `_security/oidc/prepare` and `_security/oidc/authenticate` APIs responses (#64966)

* This change adds realm name of the realm used to perform authentication to the responses of _security/oidc/authenticate and _security/oidc/authenticate APIs

Resolves #53161

* This change adds realm name of the realm used to perform authentication to the responses of _security/oidc/authenticate and _security/oidc/authenticate APIs

Resolves #53161

* This change adds realm name of the realm used to perform authentication to the responses of _security/oidc/authenticate and _security/oidc/authenticate APIs

Resolves #53161

* This change adds realm name of the realm used to perform authentication to the responses of _security/oidc/authenticate and _security/oidc/authenticate APIs

Resolves #53161

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

x-pack/docs/en/rest-api/security/oidc-authenticate-api.asciidoc

@@ -58,7 +58,7 @@ be used to authenticate this. Useful when multiple realms have been defined.
 
 The following example request exchanges the response that was returned from the
 OpenID Connect Provider after a successful authentication, for an {es} access
-token and refresh token to be used in subsequent requests. This example is from 
+token and refresh token to be used in subsequent requests. This example is from
 an authentication that uses the authorization code grant flow.
 
 [source,console]

x-pack/docs/en/rest-api/security/oidc-prepare-authentication-api.asciidoc

@@ -3,7 +3,7 @@
 === OpenID Connect Prepare Authentication API
 
 Creates an oAuth 2.0 authentication request as a URL string based on the
-configuration of the respective OpenID Connect authentication realm in {es}. 
+configuration of the respective OpenID Connect authentication realm in {es}.
 
 [[security-api-oidc-prepare-authentication-request]]
 ==== {api-request-title}
@@ -16,13 +16,13 @@ configuration of the respective OpenID Connect authentication realm in {es}.
 [[security-api-oidc-prepare-authentication-desc]]
 ==== {api-description-title}
 
-The response of this API is a URL pointing to the Authorization Endpoint of the 
-configured OpenID Connect Provider and can be used to redirect the browser of 
+The response of this API is a URL pointing to the Authorization Endpoint of the
+configured OpenID Connect Provider and can be used to redirect the browser of
 the user in order to continue the authentication process.
 
 {es} exposes all the necessary OpenID Connect related functionality via the
 OpenID Connect APIs. These APIs are used internally by {kib} in order to provide
-OpenID Connect based authentication, but can also be used by other, custom web 
+OpenID Connect based authentication, but can also be used by other, custom web
 applications or other clients. See also
 <<security-api-oidc-authenticate,OpenID Connect authenticate API>>
 and <<security-api-oidc-logout,OpenID Connect logout API>>.
@@ -81,7 +81,8 @@ the Authentication Request, as HTTP GET parameters:
 {
   "redirect" : "http://127.0.0.1:8080/c2id-login?scope=openid&response_type=id_token&redirect_uri=https%3A%2F%2Fmy.fantastic.rp%2Fcb&state=4dbrihtIAt3wBTwo6DxK-vdk-sSyDBV8Yf0AjdkdT5I&nonce=WaBPH0KqPVdG5HHdSxPRjfoZbXMCicm5v1OiAj0DUFM&client_id=elasticsearch-rp",
   "state" : "4dbrihtIAt3wBTwo6DxK-vdk-sSyDBV8Yf0AjdkdT5I",
-  "nonce" : "WaBPH0KqPVdG5HHdSxPRjfoZbXMCicm5v1OiAj0DUFM"
+  "nonce" : "WaBPH0KqPVdG5HHdSxPRjfoZbXMCicm5v1OiAj0DUFM",
+  "realm" : "oidc1"
 }
 --------------------------------------------------
 // TESTRESPONSE[s/4dbrihtIAt3wBTwo6DxK-vdk-sSyDBV8Yf0AjdkdT5I/\$\{body.state\}/]
@@ -109,7 +110,8 @@ the Authentication Request, as HTTP GET parameters:
 {
   "redirect" : "http://127.0.0.1:8080/c2id-login?scope=openid&response_type=id_token&redirect_uri=https%3A%2F%2Fmy.fantastic.rp%2Fcb&state=lGYK0EcSLjqH6pkT5EVZjC6eIW5YCGgywj2sxROO&nonce=zOBXLJGUooRrbLbQk5YCcyC8AXw3iloynvluYhZ5&client_id=elasticsearch-rp",
   "state" : "lGYK0EcSLjqH6pkT5EVZjC6eIW5YCGgywj2sxROO",
-  "nonce" : "zOBXLJGUooRrbLbQk5YCcyC8AXw3iloynvluYhZ5"
+  "nonce" : "zOBXLJGUooRrbLbQk5YCcyC8AXw3iloynvluYhZ5",
+  "realm" : "oidc1"
 }
 --------------------------------------------------
 
@@ -134,8 +136,9 @@ the Authentication Request, as HTTP GET parameters:
 {
   "redirect" : "http://127.0.0.1:8080/c2id-login?login_hint=this_is_an_opaque_string&scope=openid&response_type=id_token&redirect_uri=https%3A%2F%2Fmy.fantastic.rp%2Fcb&state=4dbrihtIAt3wBTwo6DxK-vdk-sSyDBV8Yf0AjdkdT5I&nonce=WaBPH0KqPVdG5HHdSxPRjfoZbXMCicm5v1OiAj0DUFM&client_id=elasticsearch-rp",
   "state" : "4dbrihtIAt3wBTwo6DxK-vdk-sSyDBV8Yf0AjdkdT5I",
-  "nonce" : "WaBPH0KqPVdG5HHdSxPRjfoZbXMCicm5v1OiAj0DUFM"
+  "nonce" : "WaBPH0KqPVdG5HHdSxPRjfoZbXMCicm5v1OiAj0DUFM",
+  "realm" : "oidc1"
 }
 --------------------------------------------------
 // TESTRESPONSE[s/4dbrihtIAt3wBTwo6DxK-vdk-sSyDBV8Yf0AjdkdT5I/\$\{body.state\}/]
-// TESTRESPONSE[s/WaBPH0KqPVdG5HHdSxPRjfoZbXMCicm5v1OiAj0DUFM/\$\{body.nonce\}/]
+// TESTRESPONSE[s/WaBPH0KqPVdG5HHdSxPRjfoZbXMCicm5v1OiAj0DUFM/\$\{body.nonce\}/]

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/action/oidc/OpenIdConnectPrepareAuthenticationResponse.java

@@ -5,6 +5,7 @@
  */
 package org.elasticsearch.xpack.core.security.action.oidc;
 
+import org.elasticsearch.Version;
 import org.elasticsearch.action.ActionResponse;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -28,11 +29,16 @@ public class OpenIdConnectPrepareAuthenticationResponse extends ActionResponse i
      * String value used to associate a Client session with an ID Token, and to mitigate replay attacks.
      */
     private String nonce;
+    /*
+     * String value: name of the realm used to perform authentication.
+     */
+    private String realmName;
 
-    public OpenIdConnectPrepareAuthenticationResponse(String authorizationEndpointUrl, String state, String nonce) {
+    public OpenIdConnectPrepareAuthenticationResponse(String authorizationEndpointUrl, String state, String nonce, String realmName) {
         this.authenticationRequestUrl = authorizationEndpointUrl;
         this.state = state;
         this.nonce = nonce;
+        this.realmName = realmName;
     }
 
     public OpenIdConnectPrepareAuthenticationResponse(StreamInput in) throws IOException {
@@ -40,6 +46,9 @@ public class OpenIdConnectPrepareAuthenticationResponse extends ActionResponse i
         authenticationRequestUrl = in.readString();
         state = in.readString();
         nonce = in.readString();
+        if (in.getVersion().onOrAfter(Version.V_7_11_0)) {
+            realmName = in.readString();
+        }
     }
 
     public String getAuthenticationRequestUrl() {
@@ -54,15 +63,23 @@ public class OpenIdConnectPrepareAuthenticationResponse extends ActionResponse i
         return nonce;
     }
 
+    public String getRealmName() {
+        return realmName;
+    }
+
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         out.writeString(authenticationRequestUrl);
         out.writeString(state);
         out.writeString(nonce);
+        if (out.getVersion().onOrAfter(Version.V_7_11_0)) {
+            out.writeString(realmName);
+        }
     }
 
     public String toString() {
-        return "{authenticationRequestUrl=" + authenticationRequestUrl + ", state=" + state + ", nonce=" + nonce + "}";
+        return "{authenticationRequestUrl=" + authenticationRequestUrl + ", state=" + state + ", nonce="
+            + nonce + ", realmName" + realmName + "}";
     }
 
     @Override
@@ -71,6 +88,9 @@ public class OpenIdConnectPrepareAuthenticationResponse extends ActionResponse i
         builder.field("redirect", authenticationRequestUrl);
         builder.field("state", state);
         builder.field("nonce", nonce);
+        if(realmName != null){
+            builder.field("realm", realmName);
+        }
         builder.endObject();
         return builder;
     }

x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/authc/oidc/OpenIdConnectRealm.java

@@ -363,7 +363,7 @@ public class OpenIdConnectRealm extends Realm implements Releasable {
             builder.loginHint(loginHint);
         }
         return new OpenIdConnectPrepareAuthenticationResponse(builder.build().toURI().toString(),
-            state.getValue(), nonce.getValue());
+            state.getValue(), nonce.getValue(), this.name());
     }
 
     public boolean isIssuerValid(String issuer) {

x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/authc/oidc/OpenIdConnectRealmTests.java

@@ -269,6 +269,7 @@ public class OpenIdConnectRealmTests extends OpenIdConnectTestCase {
         assertThat(response.getAuthenticationRequestUrl(),
             equalTo("https://op.example.com/login?scope=scope1+scope2+openid&response_type=code" +
                 "&redirect_uri=https%3A%2F%2Frp.my.com%2Fcb&state=" + state + "&nonce=" + nonce + "&client_id=rp-my"));
+        assertThat(response.getRealmName(), equalTo(REALM_NAME));
     }
 
     public void testBuildingAuthenticationRequest() {
@@ -292,6 +293,7 @@ public class OpenIdConnectRealmTests extends OpenIdConnectTestCase {
         assertThat(response.getAuthenticationRequestUrl(),
             equalTo("https://op.example.com/login?scope=openid+scope1+scope2&response_type=code" +
                 "&redirect_uri=https%3A%2F%2Frp.my.com%2Fcb&state=" + state + "&nonce=" + nonce + "&client_id=rp-my"));
+        assertThat(response.getRealmName(), equalTo(REALM_NAME));
     }
 
     public void testBuilidingAuthenticationRequestWithDefaultScope() {
@@ -313,6 +315,7 @@ public class OpenIdConnectRealmTests extends OpenIdConnectTestCase {
         final String nonce = response.getNonce();
         assertThat(response.getAuthenticationRequestUrl(), equalTo("https://op.example.com/login?scope=openid&response_type=code" +
             "&redirect_uri=https%3A%2F%2Frp.my.com%2Fcb&state=" + state + "&nonce=" + nonce + "&client_id=rp-my"));
+        assertThat(response.getRealmName(), equalTo(REALM_NAME));
     }
 
     public void testBuildLogoutResponse() throws Exception {
@@ -370,6 +373,7 @@ public class OpenIdConnectRealmTests extends OpenIdConnectTestCase {
 
         assertThat(response.getAuthenticationRequestUrl(), equalTo("https://op.example.com/login?scope=openid&response_type=code" +
             "&redirect_uri=https%3A%2F%2Frp.my.com%2Fcb&state=" + state + "&nonce=" + nonce + "&client_id=rp-my"));
+        assertThat(response.getRealmName(), equalTo(REALM_NAME));
     }
 
     public void testBuildingAuthenticationRequestWithLoginHint() {
@@ -394,6 +398,7 @@ public class OpenIdConnectRealmTests extends OpenIdConnectTestCase {
         assertThat(response.getAuthenticationRequestUrl(), equalTo("https://op.example.com/login?login_hint=" + thehint +
             "&scope=openid&response_type=code&redirect_uri=https%3A%2F%2Frp.my.com%2Fcb&state=" +
             state + "&nonce=" + nonce + "&client_id=rp-my"));
+        assertThat(response.getRealmName(), equalTo(REALM_NAME));
     }
 
     private AuthenticationResult authenticateWithOidc(String principal, UserRoleMapper roleMapper, boolean notPopulateMetadata,