source: vendor/3.6.25/docs-xml/smbdotconf/security/authmethods.xml

<samba:parameter name="auth methods"
                 context="G"
                                 type="list"
                 basic="1" advanced="1" wizard="1" developer="1"
                 xmlns:samba="http://www.samba.org/samba/DTD/samba-doc">
<description>

    <para>
    This option allows the administrator to chose what authentication methods <command  moreinfo="none">smbd</command> 
    will use when authenticating a user. This option defaults to sensible values based on <smbconfoption name="security"/>.  
    This should be considered a developer option and used only in rare circumstances.  In the majority (if not all) 
    of production servers, the default setting should be adequate.
    </para>

    <para>
    Each entry in the list attempts to authenticate the user in turn, until
    the user authenticates.  In practice only one method will ever actually 
    be able to complete the authentication.
    </para>

    <para>
    Possible options include <constant>guest</constant> (anonymous access), 
    <constant>sam</constant> (lookups in local list of accounts based on netbios 
    name or domain name), <constant>winbind</constant> (relay authentication requests
    for remote users through winbindd), <constant>ntdomain</constant> (pre-winbindd 
    method of authentication for remote domain users; deprecated in favour of winbind method), 
    <constant>trustdomain</constant> (authenticate trusted users by contacting the 
    remote DC directly from smbd; deprecated in favour of winbind method).
    </para>

</description>
<value type="default"/>
<value type="example">guest sam winbind</value>
</samba:parameter>