diff --git a/pkg/jmap/http.go b/pkg/jmap/http.go
index c9fcef0dcb..054fd4172c 100644
--- a/pkg/jmap/http.go
+++ b/pkg/jmap/http.go
@@ -104,14 +104,22 @@ func NewMasterAuthHttpJmapClientAuthenticator(masterUser string, masterPassword
 var _ HttpJmapClientAuthenticator = &MasterAuthHttpJmapClientAuthenticator{}
 
 func (h *MasterAuthHttpJmapClientAuthenticator) Authenticate(ctx context.Context, username string, _ *log.Logger, req *http.Request) Error {
-	masterUsername := username + "%" + h.masterUser
-	req.SetBasicAuth(masterUsername, h.masterPassword)
+	if username == h.masterUser {
+		req.SetBasicAuth(username, h.masterPassword)
+	} else {
+		masterUsername := username + "%" + h.masterUser
+		req.SetBasicAuth(masterUsername, h.masterPassword)
+	}
 	return nil
 }
 
 func (h *MasterAuthHttpJmapClientAuthenticator) AuthenticateWS(ctx context.Context, username string, _ *log.Logger, headers http.Header) Error {
-	masterUsername := username + "%" + h.masterUser
-	headers.Add("Authorization", "Basic "+base64.StdEncoding.EncodeToString([]byte(masterUsername+":"+h.masterPassword)))
+	if username == h.masterUser {
+		headers.Add("Authorization", "Basic "+base64.StdEncoding.EncodeToString([]byte(username+":"+h.masterPassword)))
+	} else {
+		masterUsername := username + "%" + h.masterUser
+		headers.Add("Authorization", "Basic "+base64.StdEncoding.EncodeToString([]byte(masterUsername+":"+h.masterPassword)))
+	}
 	return nil
 }