fix: check grant types and add refresh token to discovery

pkg/op/op.go

@@ -84,6 +84,7 @@ type Config struct {
 	DefaultLogoutRedirectURI string
 	CodeMethodS256           bool
 	AuthMethodPrivateKeyJWT  bool
+	GrantTypeRefreshToken    bool
 }
 
 type endpoints struct {
@@ -189,6 +190,10 @@ func (o *openidProvider) AuthMethodPrivateKeyJWTSupported() bool {
 	return o.config.AuthMethodPrivateKeyJWT
 }
 
+func (o *openidProvider) GrantTypeRefreshTokenSupported() bool {
+	return o.config.GrantTypeRefreshToken
+}
+
 func (o *openidProvider) GrantTypeTokenExchangeSupported() bool {
 	return false
 }