REDHAT-BUG-2357738: High severity Openid mod_auth_openidc vulnerability

modauthopenidc is an OpenID Certified authentication and authorization module for the Apache 2.x HTTP server that implements the OpenID Connect Relying Party functionality. Prior to 2.4.16.11, a bug in a modauthopenidc results in disclosure of protected content to unauthenticated users. The conditions for disclosure are an OIDCProviderAuthRequestMethod POST, a valid account, and there mustn't be any application-level gateway (or load balancer etc) protecting the server. When you request a protected resource, the response includes the HTTP status, the HTTP headers, the intended response (the self-submitting form), and the protected resource (with no headers). This is an example of a request for a protected resource, including all the data returned. In the case where modauthopenidc returns a form, it has to return OK from checkuserid so as not to go down the error path in httpd. This means httpd will try to issue the protected resource. oidccontenthandler is called early, which has the opportunity to prevent the normal output being issued by httpd. oidccontenthandler has a number of checks for when it intervenes, but it doesn't check for this case, so the handler returns DECLINED. Consequently, httpd appends the protected content to the response. The issue has been patched in modauthopenidc versions >= 2.4.16.11.