Fix the error message when the token is incorrect (#25701)

we refactored `userIDFromToken` for the token parsing part into a new
function `parseToken`. `parseToken` returns the string `token` from
request, and a boolean `ok` representing whether the token exists or
not. So we can distinguish between token non-existence and token
inconsistency in the `verfity` function, thus solving the problem of no
proper error message when the token is inconsistent.
close #24439  
related #22119

---------

Co-authored-by: Jason Song <i@wolfogre.com>
Co-authored-by: Giteabot <teabot@gitea.io>

2 files changed, 41 insertions, 24 deletions

diff --git a/services/auth/group.go b/services/auth/group.go
index a1ff65f203..7193dfcf49 100644
--- a/services/auth/group.go
+++ b/services/auth/group.go
@@ -49,12 +49,22 @@ func (b *Group) Name() string {
 // Verify extracts and validates
 func (b *Group) Verify(req *http.Request, w http.ResponseWriter, store DataStore, sess SessionStore) (*user_model.User, error) {
 	// Try to sign in with each of the enabled plugins
+	var retErr error
 	for _, ssoMethod := range b.methods {
 		user, err := ssoMethod.Verify(req, w, store, sess)
 		if err != nil {
-			return nil, err
+			if retErr == nil {
+				retErr = err
+			}
+			// Try other methods if this one failed.
+			// Some methods may share the same protocol to detect if they are matched.
+			// For example, OAuth2 and conan.Auth both read token from "Authorization: Bearer <token>" header,
+			// If OAuth2 returns error, we should give conan.Auth a chance to try.
+			continue
 		}
 
+		// If any method returns a user, we can stop trying.
+		// Return the user and ignore any error returned by previous methods.
 		if user != nil {
 			if store.GetData()["AuthedMethod"] == nil {
 				if named, ok := ssoMethod.(Named); ok {
@@ -65,5 +75,6 @@ func (b *Group) Verify(req *http.Request, w http.ResponseWriter, store DataStore
 		}
 	}
 
-	return nil, nil
+	// If no method returns a user, return the error returned by the first method.
+	return nil, retErr
 }
diff --git a/services/auth/oauth2.go b/services/auth/oauth2.go
index b70f84da9b..0dd7a12d2c 100644
--- a/services/auth/oauth2.go
+++ b/services/auth/oauth2.go
@@ -59,31 +59,32 @@ func (o *OAuth2) Name() string {
 	return "oauth2"
 }
 
-// userIDFromToken returns the user id corresponding to the OAuth token.
-// It will set 'IsApiToken' to true if the token is an API token and
-// set 'ApiTokenScope' to the scope of the access token
-func (o *OAuth2) userIDFromToken(req *http.Request, store DataStore) int64 {
+// parseToken returns the token from request, and a boolean value
+// representing whether the token exists or not
+func parseToken(req *http.Request) (string, bool) {
 	_ = req.ParseForm()
-
+	// Check token.
+	if token := req.Form.Get("token"); token != "" {
+		return token, true
+	}
 	// Check access token.
-	tokenSHA := req.Form.Get("token")
-	if len(tokenSHA) == 0 {
-		tokenSHA = req.Form.Get("access_token")
-	}
-	if len(tokenSHA) == 0 {
-		// Well, check with header again.
-		auHead := req.Header.Get("Authorization")
-		if len(auHead) > 0 {
-			auths := strings.Fields(auHead)
-			if len(auths) == 2 && (auths[0] == "token" || strings.ToLower(auths[0]) == "bearer") {
-				tokenSHA = auths[1]
-			}
-		}
+	if token := req.Form.Get("access_token"); token != "" {
+		return token, true
 	}
-	if len(tokenSHA) == 0 {
-		return 0
+	// check header token
+	if auHead := req.Header.Get("Authorization"); auHead != "" {
+		auths := strings.Fields(auHead)
+		if len(auths) == 2 && (auths[0] == "token" || strings.ToLower(auths[0]) == "bearer") {
+			return auths[1], true
+		}
 	}
+	return "", false
+}
 
+// userIDFromToken returns the user id corresponding to the OAuth token.
+// It will set 'IsApiToken' to true if the token is an API token and
+// set 'ApiTokenScope' to the scope of the access token
+func (o *OAuth2) userIDFromToken(tokenSHA string, store DataStore) int64 {
 	// Let's see if token is valid.
 	if strings.Contains(tokenSHA, ".") {
 		uid := CheckOAuthAccessToken(tokenSHA)
@@ -129,10 +130,15 @@ func (o *OAuth2) Verify(req *http.Request, w http.ResponseWriter, store DataStor
 		return nil, nil
 	}
 
-	id := o.userIDFromToken(req, store)
+	token, ok := parseToken(req)
+	if !ok {
+		return nil, nil
+	}
+
+	id := o.userIDFromToken(token, store)
 
 	if id <= 0 && id != -2 { // -2 means actions, so we need to allow it.
-		return nil, nil
+		return nil, user_model.ErrUserNotExist{}
 	}
 	log.Trace("OAuth2 Authorization: Found token for user[%d]", id)