[PP-1] Support OpenID Connect Discovery

Looks like there's a module that provides this for the OAuth2 server module: https://www.drupal.org/project/openid_connect_autodiscovery →

There is also on for simple_oauth module:
https://github.com/sanduhrs/drupal-openid_connect_discovery

Any reason not to bring this into the simple_oauth module?

AFAICT there are two branches, but no MR yet. That would be the first step. After that it will depend on maintainer's availability & priorities.

Hello,

Issuer shoudn't have a trailing slash at the END

https://www.linkedin.com/oauth/.well-known/openid-configuration
"issuer" : "https://www.linkedin.com",

https://accounts.google.com/.well-known/openid-configuration
"issuer": "https://accounts.google.com",

In our case

      'issuer' => trim(Url::fromUri('internal:/')->setAbsolute()->toString(), '/'),

should be replaced with

      'issuer' => trim(Url::fromUri('internal:/')->setAbsolute()->toString()),

Also, jwks_uri should be accessible to Anonymous users but settings _access: 'TRUE' is not enought. We need to alter some code in the Controller handle() function

if (!$this->user instanceof TokenAuthUser) {
throw new AccessDeniedHttpException('This route is only available for authenticated requests using OAuth2.');
}

should be removed