fix generateDocs

uaa/src/test/java/org/cloudfoundry/identity/uaa/mock/providers/IdentityProviderEndpointDocs.java

@@ -136,7 +136,7 @@ class IdentityProviderEndpointDocs extends EndpointDocs {
             ATTRIBUTE_MAPPING_CUSTOM_ATTRIBUTES_DEPARTMENT
     };
 
-    private FieldDescriptor relyingPartySecret = fieldWithPath("config.relyingPartySecret").optional().type(STRING).description("The client secret of the relying party at the external OAuth provider. If not set, the external OAuth client is treated as public client, then the flow is protected with [PKCE](https://tools.ietf.org/html/rfc7636) using code challenge method `S256`.");
+    private FieldDescriptor relyingPartySecret = fieldWithPath("config.relyingPartySecret").constrained("Required if the external client is confidential.").type(STRING).description("The client secret of the relying party at the external OAuth provider. If not set, the external OAuth client is treated as public client, then the flow is protected with [PKCE](https://tools.ietf.org/html/rfc7636) using code challenge method `S256`.");
 
     private static InMemoryLdapServer ldapContainer;