Configure Kerberos SSO on Moodle: KRB5KDC_ERR_PREAUTH_REQUIRED

I'm trying to set up kerberos SSO in Moodle but I'm getting a error_code: KRB5KDC_ERR_PREAUTH_REQUIRED (25): **1) I've configured kerberos on Apache:** installed kerberos, configured via /etc/krb5.cnf, and tested via kinit command getting right kerberos tickets. WORKS **2) I've created a virtual host in Apache with a folder with kerberos authentication for testing:** create a keytab file, tested authentication through kerberos works in the testing virtual site. I get the LDAP REMOTE_USER info and passes the authentication, also kerberos traffic is generated (fetched kerberos traffic with wireshark). WORKS **3) Configured virtual host to use kerberos to authenticate to moodle:** as shown in moodle documentation. [Moodle Kerberos SSO documentation][1] **4) Configured moodle's LDAP auth plugin:** login with an LDAP user works fine. WORKS **5) Configured NTLM options in moodle's ldap plugin:** I've tested and it does generate kerberos authentication network traffic (fetched kerberos with wireshark). But I'm getting a **KRB5KDC_ERR_PREAUTH_REQUIRED (25)**. Moodle LDAP configuration (NTLM section): Enable = yes Subnetwork = 192.168.0.0/16 Authentication type = kerberos Username format = (none) ![moodle ldap config ntlm section][2] My virtual host configuration for both sites (test folder and moodle folder) is: <VirtualHost *:80> # General ServerAdmin myemail@domain.com DocumentRoot /home/moodle/moodle ServerName mymoodle.es LogLevel debug ErrorLog logs/testing-error.log CustomLog logs/testing.log combined <Location /krb_testing> ## Redes para las que se ofrece SSO AuthType Kerberos AuthName "Kerberos Login" KrbMethodNegotiate On KrbMethodK5Passwd Off KrbServiceName HTTP/mymoodle.es@MYREALM.DOMAIN.ES KrbAuthRealms MYREALM.DOMAIN.ES Krb5KeyTab /etc/krb5.keytab ## Sin require valid-user no se produce la negociacion require valid-user </Location> <Directory /home/moodle/moodle/auth/ldap/> <Files ntlmsso_magic.php> AuthName "Moodle" AuthType Kerberos KrbAuthRealms MYREALM.DOMAIN.ES KrbServiceName HTTP/mymoodle.es@MYREALM.DOMAIN.ES Krb5KeyTab /etc/krb5.keytab KrbMethodNegotiate on KrbMethodK5Passwd on KrbAuthoritative on require valid-user </Files> </Directory> </VirtualHost> **Apache version:** Apache/2.2.15 (CentOS) **Moodle version:** 2.4.7 [1]: http://docs.moodle.org/22...