My Apache ask for the username and password when a went to the admin interface. After a successful Basic authentication I get the unwanted LimeSurvey login screen.

Apache 2.4 config snippet:
<Directory /opt/limesurvey>
<If "%{PATH_INFO} =~ m#/admin#">
AuthType Basic
AuthName "Account"
require valid-user
</If>
</Directory>

Limesurvey config.php snippet:
return array(
...
'auth_webserver'=>true,
'auth_webserver_user_map' => Array('xxxxx' => 'admin'),
'auth_webserver_autocreate_user'=>true,
'auth_webserver_autocreate_profile' => Array(
'full_name' => preg_match('/@/',$_SERVER['REMOTE_USER']) ? strtok($_SERVER['REMOTE_USER'],'@') : $_SERVER['REMOTE_USER'],
'email' => preg_match('/@/',$_SERVER['REMOTE_USER'])? $_SERVER['REMOTE_USER'] : $_SERVER['REMOTE_USER'].'@mydomain.de',
'lang' => 'en',
'htmleditormode' => 'inline',
'templatelist' => 'default,basic,bluengrey,citronade,clear_logo,eirenicon,limespired,mint_idea,sherpa,vallendar',
'create_survey' => 1,
'create_user' => 0,
'delete_user' => 0,
'superadmin' => 0,
'configurator' => 0,
'manage_template' => 0,
'manage_label' => 0
),

...
);