support the username returned by Synology DSM SSO Server during OIDC authentication (#449)

pkg/auth/oauth2/provider/oidc/oidc_provider.go

@@ -19,6 +19,7 @@ import (
 // OIDCClaims represents OIDC claims
 type OIDCClaims struct {
 	PreferredUserName string `json:"preferred_username"`
+	UserName          string `json:"username"`
 	Name              string `json:"name"`
 	Email             string `json:"email"`
 }
@@ -113,6 +114,10 @@ func (p *OIDCProvider) GetUserInfo(c core.Context, oauth2Token *oauth2.Token) (*
 			userName = claims.PreferredUserName
 		}
 
+		if userName == "" {
+			userName = claims.UserName
+		}
+
 		if email == "" {
 			email = claims.Email
 		}