fix(auth): retry up to three times when an auth provider cannot be reached

Resolves https://github.com/go-vikunja/vikunja/issues/2050

pkg/modules/auth/ldap/ldap.go

@@ -61,11 +61,17 @@ func InitializeLDAPConnection() {
 		log.Fatal("LDAP user filter is not configured")
 	}
 
-	l, err := ConnectAndBindToLDAPDirectory()
+	err := utils.RetryWithBackoff("LDAP server", func() error {
+		l, connErr := ConnectAndBindToLDAPDirectory()
+		if connErr == nil {
+			_ = l.Close()
+		}
+		return connErr
+	})
+
 	if err != nil {
-		log.Fatalf("Could not bind to LDAP server: %s", err)
+		log.Fatalf("Could not connect to LDAP server: %s", err)
 	}
-	_ = l.Close()
 }
 
 func ConnectAndBindToLDAPDirectory() (l *ldap.Conn, err error) {
@@ -90,7 +96,7 @@ func ConnectAndBindToLDAPDirectory() (l *ldap.Conn, err error) {
 
 	l, err = ldap.DialURL(url, opts...)
 	if err != nil {
-		log.Fatalf("Could not connect to LDAP server: %s", err)
+		return nil, fmt.Errorf("could not connect to LDAP server: %w", err)
 	}
 
 	err = l.Bind(

pkg/modules/auth/openid/openid.go

@@ -83,10 +83,16 @@ func init() {
 }
 
 func (p *Provider) setOicdProvider() (err error) {
-	p.openIDProvider, err = oidc.NewProvider(context.Background(), p.OriginalAuthURL)
+	err = utils.RetryWithBackoff(fmt.Sprintf("OpenID Connect provider '%s'", p.Name), func() error {
+		var providerErr error
+		p.openIDProvider, providerErr = oidc.NewProvider(context.Background(), p.OriginalAuthURL)
+		return providerErr
+	})
+
 	if err != nil && p.RequireAvailability {
 		log.Fatalf("OpenID Connect provider '%s' is not available and require_availability is enabled: %s", p.Name, err)
 	}
+
 	return err
 }
 

pkg/utils/retry.go

@@ -0,0 +1,50 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-present Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package utils
+
+import (
+	"time"
+
+	"code.vikunja.io/api/pkg/log"
+)
+
+// RetryWithBackoff executes the given function up to 3 times with exponential backoff.
+// Delays between retries are 1s, 2s, 4s (total max wait: 7s).
+// The name parameter is used for logging to identify what operation is being retried.
+// Returns nil on success, or the last error after all retries are exhausted.
+func RetryWithBackoff(name string, fn func() error) error {
+	const maxRetries = 3
+	baseDelay := 1 * time.Second
+
+	var err error
+	for attempt := 1; attempt <= maxRetries; attempt++ {
+		err = fn()
+		if err == nil {
+			return nil
+		}
+
+		if attempt < maxRetries {
+			delay := baseDelay * time.Duration(1<<(attempt-1)) // exponential: 1s, 2s, 4s
+			log.Warningf("%s not available (attempt %d/%d), retrying in %v: %s",
+				name, attempt, maxRetries, delay, err)
+			time.Sleep(delay)
+		}
+	}
+
+	log.Errorf("%s not available after %d attempts: %s", name, maxRetries, err)
+	return err
+}