Trying to use bearer token but unable to use firstordefault method in account controller for applicationuser table.(need tocheck user is admin or not)

Question

In account controller need to check whether user is admin or not using custom property isadmin in bearer token authentication using dot net webapi.

public bool Isadmin(string username,string password)
{
    ApplicationDbContext db = new ApplicationDbContext();
    //or default        
}