PluginProxy: Split implementations of token providers (#32820)

* Split implementations of token providers

* Fix imports

* Fix code racing in unit tests

pkg/api/pluginproxy/token_provider_gce.go

@@ -0,0 +1,41 @@
+package pluginproxy
+
+import (
+	"context"
+
+	"github.com/grafana/grafana/pkg/models"
+	"github.com/grafana/grafana/pkg/plugins"
+	"golang.org/x/oauth2/google"
+)
+
+type gceAccessTokenProvider struct {
+	datasourceId      int64
+	datasourceVersion int
+	ctx               context.Context
+	route             *plugins.AppPluginRoute
+}
+
+func newGceAccessTokenProvider(ctx context.Context, ds *models.DataSource, pluginRoute *plugins.AppPluginRoute) *gceAccessTokenProvider {
+	return &gceAccessTokenProvider{
+		datasourceId:      ds.Id,
+		datasourceVersion: ds.Version,
+		ctx:               ctx,
+		route:             pluginRoute,
+	}
+}
+
+func (provider *gceAccessTokenProvider) getAccessToken() (string, error) {
+	tokenSrc, err := google.DefaultTokenSource(provider.ctx, provider.route.JwtTokenAuth.Scopes...)
+	if err != nil {
+		logger.Error("Failed to get default token from meta data server", "error", err)
+		return "", err
+	} else {
+		token, err := tokenSrc.Token()
+		if err != nil {
+			logger.Error("Failed to get default access token from meta data server", "error", err)
+			return "", err
+		} else {
+			return token.AccessToken, nil
+		}
+	}
+}