[14.0] auth_oidc add call to validation endpoint

[stellamargonar]

add call to oauth provider validation endpoint in the auth_oidc module, as explained in #325

[ap-wtioit]

needed this to get auth_oidc working with OpenID Connect. ID Token does not contain a user_id claim. nor is user_id listed in the standard claims.

Note: the call to the validation endpoint is not necessary from OpenID Connect Authorization Code Flow (because the ID Token can be and is verified with JWKS according to https://openid.net/specs/openid-connect-core-1_0.html#rfc.section.3.1.3.7)

however auth_oidc/auth_oauth uses the non standard claim user_id which makes this necessary. but it only works (with standard claims) because auth_oauth maps sub to user_id in _auth_oauth_validate:

         subject = next(filter(None, [
            validation.pop(key, None)
            for key in [
                'sub', # standard
                'id', # google v1 userinfo, facebook opengraph
                'user_id', # google tokeninfo, odoo (tokeninfo)
            ]
        ]), None)
        ...
        validation['user_id'] = subject

https://github.com/odoo/odoo/blob/14.0/addons/auth_oauth/models/res_users.py#L56

@stellamargonar would something like this also work for the errors you encountered in #325?

        ....
        validation = oauth_provider._parse_id_token(id_token, access_token)
        # required check
        if "sub" in validation and not "user_id" in validation:
            # set user_id for auth_oauth, user_id is not an OpenID Connect standard claim:
            # https://openid.net/specs/openid-connect-core-1_0.html#StandardClaims
            validation["user_id"] = validation["sub"]
        elif not validation.get("user_id"):
            _logger.error("user_id claim not found in id_token (after mapping).")
            raise AccessDenied()
        ...

I tested locally together with #393 in 15.0 against our oauth/openid provider.

For reference the error i encountered without this patch:

odoo_1                                                | 2022-08-09 11:45:00,364 1 ERROR devel odoo.addons.auth_oidc.models.res_users: user_id claim not found in id_token (after mapping). 
odoo_1                                                | 2022-08-09 11:45:00,364 1 INFO devel odoo.addons.auth_oauth.controllers.main: OAuth2: access denied, redirect to main page in case a valid session exists, without setting cookies