Apache Kerberos Auth file fallback

Question

I've set up a Kerberos Authentication on my Apache Server (Ubuntu 16.04 LTS) with mod_auth_kerb. The configuration is as follows :

AuthType Kerberos
AuthName "Authentication Required"
KrbAuthRealm MY.DOMAIN
Krb5KeyTab "/path/to/keytab"
KrbMethodK5Passwd On
Require valid-user

It works fine as it is.

But I want to add an authentication fallback to an .htpasswd file, in case of a Kerberos failure.

I tried the following :

AuthType Basic
AuthName "Authentication Required"
AuthBasicProvider kerberos file
KrbAuthRealm MY.DOMAIN
Krb5KeyTab "/path/to/keytab"
KrbMethodK5Passwd On
KrbAuthoritative Off
AuthUserFile /etc/apache2/.htpasswd
Require valid-user

But I have an error when restarting :

apache2[7455]: Unknown Authn provider: kerberos

I've set my Apache LogLevel to debug but I've nothing in the log file ... My mod_auth_kerb version is 5.4-2.2.

Any ideas ?

Thanks :)