fix: disable API client caching for GitHub App connections (#8850)

GitHub App installation tokens expire after ~1 hour, causing admin APIs
(remote-scopes, test-connection) to fail silently after token expiry.

This fix overrides GetHash() to return empty string for GitHub App connections,
disabling client caching and ensuring fresh tokens are fetched for each admin request.

PAT connections continue to use default caching behavior.

Fixes #8847

Author: fxgagnon

backend/plugins/github/models/connection.go

@@ -134,6 +134,16 @@ func (connection GithubConnection) TableName() string {
 	return "_tool_github_connections"
 }
 
+func (connection GithubConnection) GetHash() string {
+	if connection.AuthMethod == AppKey {
+		// GitHub App installation tokens expire after ~1 hour, disable API client caching
+		// to ensure fresh tokens are fetched for admin APIs (remote-scopes, test-connection)
+		return ""
+	}
+	// Use default caching for PAT connections (they don't expire)
+	return connection.BaseConnection.GetHash()
+}
+
 func (connection *GithubConnection) MergeFromRequest(target *GithubConnection, body map[string]interface{}) error {
 	modifiedConnection := GithubConnection{}
 	if err := helper.DecodeMapStruct(body, &modifiedConnection, true); err != nil {

backend/plugins/github/models/connection_test.go

@@ -18,6 +18,7 @@ limitations under the License.
 package models
 
 import (
+	"github.com/apache/incubator-devlake/core/models/common"
 	"github.com/apache/incubator-devlake/helpers/pluginhelper/api"
 	"testing"
 
@@ -238,3 +239,44 @@ func TestTokenTypeClassification(t *testing.T) {
 	assert.Equal(t, GithubTokenTypeFineGrained, conn.typeIs("github_pat_123"))
 	assert.Equal(t, GithubTokenTypeUnknown, conn.typeIs("some_other_token"))
 }
+
+func TestGithubConnection_GetHash(t *testing.T) {
+	tests := []struct {
+		name       string
+		connection GithubConnection
+		want       string
+	}{
+		{
+			name: "GitHub App connection should return empty hash to disable caching",
+			connection: GithubConnection{
+				GithubConn: GithubConn{
+					MultiAuth: api.MultiAuth{
+						AuthMethod: AppKey,
+					},
+				},
+			},
+			want: "",
+		},
+		{
+			name: "PAT connection should use default hash",
+			connection: GithubConnection{
+				BaseConnection: api.BaseConnection{
+					Model: common.Model{
+						ID: 123,
+					},
+				},
+				GithubConn: GithubConn{
+					MultiAuth: api.MultiAuth{
+						AuthMethod: AccessToken,
+					},
+				},
+			},
+			want: "1230001-01-01 00:00:00 +0000 UTC", // ID + zero UpdatedAt
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equalf(t, tt.want, tt.connection.GetHash(), "GetHash()")
+		})
+	}
+}