Sorry, I forgot to include the following. I believe my usage follows /usr/share/doc/libapache2-mod-auth-pam/README.Debian as below:
/etc/apache2/conf.d/squirrelmail.conf -> ../../squirrelmail/apache.conf ,----[ squirrelmail/apache.conf ] Alias /squirrelmail /usr/share/squirrelmail <Directory /usr/share/squirrelmail> [...] AuthPAM_Enabled on AuthType Basic AuthName "PAM" require valid-user [...] `---- jam
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