How do I add fields to the AspNetUsers table in Asp.Net Identity Framework?

You can simply open the database from App_Start folder and modify the fields. (In case your using the template)

public class ApplicationUser : IdentityUser
{
    public string YourProperyHere { get; set; }

    public async Task<ClaimsIdentity> GenerateUserIdentityAsync(UserManager<ApplicationUser> manager)
    {
        // Note the authenticationType must match the one defined in CookieAuthenticationOptions.AuthenticationType
        var userIdentity = await manager.CreateIdentityAsync(this, DefaultAuthenticationTypes.ApplicationCookie);
        // Add custom user claims here
        return userIdentity;
    }
}

Read more here

The Visitor class is provided for you as a template when you setup a new Identity Framework project, and that class is tied to the AspNetUsers table. It inherits a bunch of properties you have weak/no control over, and then you can just add whatever you want.

public class Visitor : IdentityUser
{
    [MaxLength(300)]
    public string FirstName { get; set; }

    [MaxLength(300)]
    public string LastName { get; set; }

    public DateTime CreatedOn { get; set; }


    public Visitor()
    {
        CreatedOn = DateTime.UtcNow;
    }
}

I have not yet found a way to modify or even directly query the AspNetUserLogins table, as the default Identity Framework setup gives you a db with access to Users and Roles, but not Logins. Further the table is there as a step down from Users, but, that isn't going to let you query it. And, you're at least by default stuck with the stock class that comes with Identity Framework; subclassing it and getting the framework to use that subclass may be off the table. Don't know, worth its own question:

Add Columns/Properties to AspNetUserLogins/Logins in IdentityDbContext