Where crypt is:
0 (or "plain") = No encryption. Passwords stored in plaintext.
HIGHLY DISCOURAGED.

1 (or "Y") = Use crypt(3) function.

2 (or "mysql") = Use MySQL PASSWORD() function. It is possible
that the encryption function used by PAM-MySQL
is different from that of the MySQL server, as
PAM-MySQL uses the function defined in MySQL's
C-client API instead of using PASSWORD() SQL function
in the query.

3 (or "md5") = Use plain hex MD5.

4 (or "sha1") = Use plain hex SHA1.