[raizo11]

new const usersteam[][] =
{
    "STEAM_0:1:123456789",
    "STEAM_0:1:1337"
}


new Szsteam

get_user_authid( id, Szsteam, 31 );

for(new i = 0; i < sizeof(usersteam);i++)
{
    if(equal(Szsteam,  usersteam[i]))
    {
        // your code
    }   
}