Allow For New Identity Provider Field

This commit updates the OAuth2 configuration to allow for the new 'Issuer' field.

Author: twoseat

cloudfoundry-client/src/main/java/org/cloudfoundry/uaa/identityproviders/_OAuth2Configuration.java

@@ -35,4 +35,11 @@ abstract class _OAuth2Configuration extends AbstractAuthenticationConfiguration
     @Nullable
     abstract String getCheckTokenUrl();
 
+    /**
+     * The OAuth 2.0 token issuer.
+     */
+    @JsonProperty("issuer")
+    @Nullable
+    abstract String getIssuer();
+
 }