feat: specify supported grant tyoes

internal/oauth/openid.go

@@ -9,11 +9,12 @@ import (
 
 func (h *OAuthHandler) OpenIdConfiguration(w http.ResponseWriter, r *http.Request) {
 	type Response struct {
-		TokenEndpoint         string `json:"token_endpoint"`
-		AuthorizationEndpoint string `json:"authorization_endpoint"`
-		JwksURI               string `json:"jwks_uri"`
-		Issuer                string `json:"issuer"`
-		EndSessionEndpoint    string `json:"end_session_endpoint"`
+		TokenEndpoint         string   `json:"token_endpoint"`
+		AuthorizationEndpoint string   `json:"authorization_endpoint"`
+		JwksURI               string   `json:"jwks_uri"`
+		Issuer                string   `json:"issuer"`
+		EndSessionEndpoint    string   `json:"end_session_endpoint"`
+		GrantTypesSupported   []string `json:"grant_types_supported"`
 	}
 
 	w.Header().Set("Content-Type", "application/json")
@@ -28,6 +29,10 @@ func (h *OAuthHandler) OpenIdConfiguration(w http.ResponseWriter, r *http.Reques
 		JwksURI:               h.cfg.Uri + "/.well-known/jwks.json",
 		Issuer:                h.cfg.Uri,
 		EndSessionEndpoint:    h.cfg.Uri + "/api/v1/oauth/logout",
+		GrantTypesSupported: []string{
+			"authorization_code",
+			"refresh_token",
+		},
 	}); err != nil {
 		web.Error(w, "failed to encode response", http.StatusInternalServerError)
 	}