An OpenID feature is available inside Chamilo. It is not as complete as other OpenID implementations around, but if you want to enable it you will have to follow a series of steps:
enable the OpenID login in the Portal settings page, Security section
make the OpenID field editable by the user from the Portal settings, Users section
each user will need to indicate and save his own OpenID identifier in his profile.
Work has been started to improve this, but it is likely to only be available in Chamilo 1.10 (because it requires database changes).