allow the actions user to login via the jwt token (#32527)

We have some actions that leverage the Gitea API that began receiving
401 errors, with a message that the user was not found. These actions
use the `ACTIONS_RUNTIME_TOKEN` env var in the actions job to
authenticate with the Gitea API. The format of this env var in actions
jobs changed with go-gitea/gitea/pull/28885 to be a JWT (with a
corresponding update to `act_runner`) Since it was a JWT, the OAuth
parsing logic attempted to parse it as an OAuth token, and would return
user not found, instead of falling back to look up the running task and
assigning it to the actions user.

Make ACTIONS_RUNTIME_TOKEN in action runners could be used,
attempting to parse Oauth JWTs. The code to parse potential old
`ACTION_RUNTIME_TOKEN` was kept in case someone is running an older
version of act_runner that doesn't support the Actions JWT.

services/auth/oauth2.go

@@ -17,6 +17,7 @@ import (
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/timeutil"
 	"code.gitea.io/gitea/modules/web/middleware"
+	"code.gitea.io/gitea/services/actions"
 	"code.gitea.io/gitea/services/oauth2_provider"
 )
 
@@ -54,6 +55,18 @@ func CheckOAuthAccessToken(ctx context.Context, accessToken string) int64 {
 	return grant.UserID
 }
 
+// CheckTaskIsRunning verifies that the TaskID corresponds to a running task
+func CheckTaskIsRunning(ctx context.Context, taskID int64) bool {
+	// Verify the task exists
+	task, err := actions_model.GetTaskByID(ctx, taskID)
+	if err != nil {
+		return false
+	}
+
+	// Verify that it's running
+	return task.Status == actions_model.StatusRunning
+}
+
 // OAuth2 implements the Auth interface and authenticates requests
 // (API requests only) by looking for an OAuth token in query parameters or the
 // "Authorization" header.
@@ -97,6 +110,16 @@ func parseToken(req *http.Request) (string, bool) {
 func (o *OAuth2) userIDFromToken(ctx context.Context, tokenSHA string, store DataStore) int64 {
 	// Let's see if token is valid.
 	if strings.Contains(tokenSHA, ".") {
+		// First attempt to decode an actions JWT, returning the actions user
+		if taskID, err := actions.TokenToTaskID(tokenSHA); err == nil {
+			if CheckTaskIsRunning(ctx, taskID) {
+				store.GetData()["IsActionsToken"] = true
+				store.GetData()["ActionsTaskID"] = taskID
+				return user_model.ActionsUserID
+			}
+		}
+
+		// Otherwise, check if this is an OAuth access token
 		uid := CheckOAuthAccessToken(ctx, tokenSHA)
 		if uid != 0 {
 			store.GetData()["IsApiToken"] = true