Lock goth/gothic and Re-attempt OAuth2 registration on login if registration failed at startup (#16570)

Backport #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>

models/oauth2.go

@@ -155,11 +155,6 @@ func initOAuth2LoginSources() error {
 		err := oauth2.RegisterProvider(source.Name, oAuth2Config.Provider, oAuth2Config.ClientID, oAuth2Config.ClientSecret, oAuth2Config.OpenIDConnectAutoDiscoveryURL, oAuth2Config.CustomURLMapping)
 		if err != nil {
 			log.Critical("Unable to register source: %s due to Error: %v. This source will be disabled.", source.Name, err)
-			source.IsActived = false
-			if err = UpdateSource(source); err != nil {
-				log.Critical("Unable to update source %s to disable it. Error: %v", err)
-				return err
-			}
 		}
 	}
 	return nil

modules/auth/oauth2/oauth2.go

@@ -7,6 +7,7 @@ package oauth2
 import (
 	"net/http"
 	"net/url"
+	"sync"
 
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
@@ -34,6 +35,7 @@ import (
 var (
 	sessionUsersStoreKey = "gitea-oauth2-sessions"
 	providerHeaderKey    = "gitea-oauth2-provider"
+	gothRWMutex          = sync.RWMutex{}
 )
 
 // CustomURLMapping describes the urls values to use when customizing OAuth2 provider URLs
@@ -60,6 +62,10 @@ func Init(x *xorm.Engine) 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)
+
+	gothRWMutex.Lock()
+	defer gothRWMutex.Unlock()
+
 	gothic.Store = store
 
 	gothic.SetState = func(req *http.Request) string {
@@ -82,6 +88,9 @@ func Auth(provider string, request *http.Request, response http.ResponseWriter)
 	// 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)
@@ -95,6 +104,9 @@ func ProviderCallback(provider string, request *http.Request, response http.Resp
 	// not sure if goth is thread safe (?) when using multiple providers
 	request.Header.Set(providerHeaderKey, provider)
 
+	gothRWMutex.RLock()
+	defer gothRWMutex.RUnlock()
+
 	user, err := gothic.CompleteUserAuth(response, request)
 	if err != nil {
 		return user, err
@@ -108,6 +120,9 @@ 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)
 	}
 
@@ -116,11 +131,17 @@ 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()
 }