Implement OpenID module (#599) (#1812)

* Implement OpenID module (#599)

- Unrelated: change Riot references to Element in client API routing

Signed-off-by: Bruce MacDonald <contact@bruce-macdonald.com>

* OpenID module tweaks (#599)

- specify expiry is ms rather than vague ts
- add OpenID token lifetime to configuration
- use Go naming conventions for the path params
- store plaintext token rather than hash
- remove openid table sqllite mutex

* Add default OpenID token lifetime (#599)

* Update dendrite-config.yaml

Co-authored-by: Kegsay <kegsay@gmail.com>
Co-authored-by: Kegsay <kegan@matrix.org>

federationapi/routing/routing.go

@@ -462,4 +462,10 @@ func Setup(
 			return QueryDeviceKeys(httpReq, request, keyAPI, cfg.Matrix.ServerName)
 		},
 	)).Methods(http.MethodPost)
+
+	v1fedmux.Handle("/openid/userinfo",
+		httputil.MakeExternalAPI("federation_openid_userinfo", func(req *http.Request) util.JSONResponse {
+			return GetOpenIDUserInfo(req, userAPI)
+		}),
+	).Methods(http.MethodGet)
 }