How can I setup a SOCKS proxy over ssh with password based authentication on CentOS?

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Dynamic application-level port forwarding (ssh -D) doesn’t support this feature. Take a look at the Dante for instead:

[I] net-proxy/dante
     Available versions:  1.1.19-r4 (~)1.2.3 (~)1.3.0 (~)1.3.1 (~)1.3.1-r1 (~)1.3.2 {debug kerberos pam selinux static-libs tcpd}
     Installed versions:  1.3.2(04:14:03 PM 11/08/2011)(pam static-libs tcpd -debug -kerberos -selinux)
     Homepage:            http://www.inet.no/dante/
     Description:         A free socks4,5 and msproxy implementation

But note that the password is transmitted in cleartext.

To configure username based authentication, open the /etc/sockd.conf file and add/change the following:

logoutput: syslog /var/log/dante.log

# methods for socks-rules.
method: username #rfc931

# when doing something that can require privilege, 
# it will use the userid "sockd".
user.privileged: root

# when running as usual, 
# it will use the unprivileged userid of "sockd".
user.notprivileged: sockd

pass {
    from: 0.0.0.0/0 to: 0.0.0.0/0
    protocol: tcp udp
    command: bind connect udpassociate
    log: error
    method: username
}

Check the listening sockets after starting:

# netstat -nlp | grep sockd
tcp        0      0 127.0.0.1:1080          0.0.0.0:*               LISTEN      5463/sockd          
tcp        0      0 192.168.15.36:1080      0.0.0.0:*               LISTEN      5463/sockd

Take a look at the logs file (/var/log/messages or /var/log/dante.log) if you get something wrong.

PS: the system password file (/etc/passwd) is used to verify a username and password combination.

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