Lock goth/gothic and Re-attempt OAuth2 registration on login if registration failed at startup (#16564)

This PR has two parts:

* Add locking to goth and gothic calls with a RWMutex

The goth and gothic calls are currently unlocked and thus are a cause of multiple potential races

* Reattempt OAuth2 registration on login if registration failed

If OAuth2 registration fails at startup we currently disable the login_source however an alternative approach could be to reattempt registration on login attempt.
    
Fix #16096

Signed-off-by: Andrew Thornton <art27@cantab.net>

services/auth/source/oauth2/init.go

@@ -6,6 +6,7 @@ package oauth2
 
 import (
 	"net/http"
+	"sync"
 
 	"code.gitea.io/gitea/models"
 	"code.gitea.io/gitea/modules/log"
@@ -15,6 +16,8 @@ import (
 	"github.com/markbates/goth/gothic"
 )
 
+var gothRWMutex = sync.RWMutex{}
+
 // SessionTableName is the table name that OAuth2 will use to store things
 const SessionTableName = "oauth2_session"
 
@@ -42,6 +45,10 @@ func Init() error {
 
 	// Note, when using the FilesystemStore only the session.ID is written to a browser cookie, so this is explicit for the storage on disk
 	store.MaxLength(setting.OAuth2.MaxTokenLength)
+
+	// Lock our mutex
+	gothRWMutex.Lock()
+
 	gothic.Store = store
 
 	gothic.SetState = func(req *http.Request) string {
@@ -52,6 +59,9 @@ func Init() error {
 		return req.Header.Get(ProviderHeaderKey), nil
 	}
 
+	// Unlock our mutex
+	gothRWMutex.Unlock()
+
 	return initOAuth2LoginSources()
 }
 
@@ -71,12 +81,7 @@ func initOAuth2LoginSources() error {
 		}
 		err := oauth2Source.RegisterSource()
 		if err != nil {
-			log.Critical("Unable to register source: %s due to Error: %v. This source will be disabled.", source.Name, err)
-			source.IsActive = false
-			if err = models.UpdateSource(source); err != nil {
-				log.Critical("Unable to update source %s to disable it. Error: %v", err)
-				return err
-			}
+			log.Critical("Unable to register source: %s due to Error: %v.", source.Name, err)
 		}
 	}
 	return nil

services/auth/source/oauth2/providers.go

@@ -121,6 +121,9 @@ func RegisterProvider(providerName, providerType, clientID, clientSecret, openID
 	provider, err := createProvider(providerName, providerType, clientID, clientSecret, openIDConnectAutoDiscoveryURL, customURLMapping)
 
 	if err == nil && provider != nil {
+		gothRWMutex.Lock()
+		defer gothRWMutex.Unlock()
+
 		goth.UseProviders(provider)
 	}
 
@@ -129,11 +132,17 @@ func RegisterProvider(providerName, providerType, clientID, clientSecret, openID
 
 // RemoveProvider removes the given OAuth2 provider from the goth lib
 func RemoveProvider(providerName string) {
+	gothRWMutex.Lock()
+	defer gothRWMutex.Unlock()
+
 	delete(goth.GetProviders(), providerName)
 }
 
 // ClearProviders clears all OAuth2 providers from the goth lib
 func ClearProviders() {
+	gothRWMutex.Lock()
+	defer gothRWMutex.Unlock()
+
 	goth.ClearProviders()
 }
 

services/auth/source/oauth2/source_callout.go

@@ -20,6 +20,9 @@ func (source *Source) Callout(request *http.Request, response http.ResponseWrite
 	// normally the gothic library will write some custom stuff to the response instead of our own nice error page
 	//gothic.BeginAuthHandler(response, request)
 
+	gothRWMutex.RLock()
+	defer gothRWMutex.RUnlock()
+
 	url, err := gothic.GetAuthURL(response, request)
 	if err == nil {
 		http.Redirect(response, request, url, http.StatusTemporaryRedirect)
@@ -33,6 +36,9 @@ func (source *Source) Callback(request *http.Request, response http.ResponseWrit
 	// not sure if goth is thread safe (?) when using multiple providers
 	request.Header.Set(ProviderHeaderKey, source.loginSource.Name)
 
+	gothRWMutex.RLock()
+	defer gothRWMutex.RUnlock()
+
 	user, err := gothic.CompleteUserAuth(response, request)
 	if err != nil {
 		return user, err