Your visit to IRC pretty much closes this one. :)

*** oweff (jason@greenhell.com) has joined channel #libssh2
<oweff> hi all, Pollita
<oweff> Pollita: nice work on the ssh2 bindings for php
<oweff> only i cannot get it to authenticate with a password over a connection to localhost
<oweff> ah n/m got it
*** oweff has left channel #libssh2 because ()

same problem. connect to localhost not possible.
connect to other server works.
phpscript:

<?php
$connection = ssh2_connect('localhost', 22);
if (ssh2_auth_password($connection, 'user', 'password')) {
  echo "Authentication Successful!\n";
} else {
  die('Authentication Failed...');
}
print_r($connection);

?> 

output php script:
Warning: ssh2_auth_password(): Authentication failed for ut2004 using password in /var/www/vhosts/bravo795.server4you.de/httpdocs/pages/UT2004.php on line 3
Authentication Failed...

log from ssh:
Jul  6 11:18:34 bravo795 sshd[22737]: Connection from ::ffff:127.0.0.1 port 56629
Jul  6 11:18:34 bravo795 sshd[22737]: debug1: Client protocol version 2.0; client software version libssh2_0.14 PHP
Jul  6 11:18:34 bravo795 sshd[22737]: debug1: no match: libssh2_0.14 PHP
Jul  6 11:18:34 bravo795 sshd[22737]: debug1: Enabling compatibility mode for protocol 2.0
Jul  6 11:18:34 bravo795 sshd[22737]: debug1: Local version string SSH-2.0-OpenSSH_3.8.1p1 Debian-8.sarge.4
Jul  6 11:18:34 bravo795 sshd[22737]: debug1: PAM: initializing for "ut2004"
Jul  6 11:18:34 bravo795 sshd[22737]: debug1: PAM: setting PAM_RHOST to "localhost.localdomain"
Jul  6 11:18:34 bravo795 sshd[22737]: debug1: PAM: setting PAM_TTY to "ssh"
Jul  6 11:18:34 bravo795 sshd[22737]: debug1: do_cleanup
Jul  6 11:18:35 bravo795 sshd[22737]: debug1: PAM: cleanup
Jul  6 11:18:35 bravo795 sshd[22670]: debug1: Forked child 22739.

Same problem for me... Is there still no solution for this 
problem (first report dates from more then a year ago...) 
or did I missed something?

I use Debian Stable for my server, had to 'cheat' somewhat 
at the installation of 'libssh2' (change some things in 
the src/Makefile (remove all <-o file.o> parts, add 
sometimes a '-I' at CFLAGS)) but I don't understand why 
this would allow me to connect to another PC and not to my 
localhost.

Double check your sshd_config file.  90% of the time this is because the server is pre-configured by the distribution to disable password based authentication.  It *looks* like you're using password based when you're using the command line program, but it's actually keyboard-interactive (which is an entirely different authentication scheme).

Ok, thx pollita! 

I had to allow indeed 'PasswordAuthentication' in 
sshd_config. Now it works fine!

Expected behavior then.