What's the best way to override authentication in MVC 5?

To add more columns / fields to AspNetUsers , you need to add them to Identity Model adn do Data Migration using command-update database

you can also manage keys and table name by overriding as below

 protected override void OnModelCreating(System.Data.Entity.DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<IdentityUser>().ToTable("MyUsers").Property(p => p.Id).HasColumnName("UserId");
        modelBuilder.Entity<ApplicationUser>().ToTable("MyUsers").Property(p => p.Id).HasColumnName("UserId");
        modelBuilder.Entity<IdentityUserRole>().ToTable("MyUserRoles");
        modelBuilder.Entity<IdentityUserLogin>().ToTable("MyUserLogins");
        modelBuilder.Entity<IdentityUserClaim>().ToTable("MyUserClaims");
        modelBuilder.Entity<IdentityRole>().ToTable("MyRoles");
    }

      

        
        
        
      

    

When you use ASPNET Schema to register a user, I don't think you can avoid claims, roles, and other tables, but you can just ignore them.

Update

Avoiding roles and claims in ASPNET membership

First of all create an MVC 5 application. Then execute IUser,

public class ApplicationUser : IUser
{
    public ApplicationUser()
    {
        this.Id = Guid.NewGuid().ToString();
    }
    public ApplicationUser(string userName): this()
    {
        UserName = userName;
    }
    public virtual string Id { get; set; }
    public virtual string PasswordHash { get; set; }
    public virtual string SecurityStamp { get; set; }
    public virtual string UserName { get; set; }
}

      

        
        
        
      

    

Next, we need a DbContet to store the Users,

public class ApplicationDbContext : DbContext
{
    public ApplicationDbContext()
        : base("DefaultConnection")
    {
    }
    public virtual IDbSet<ApplicationUser> Users { get; set; }
}

      

        
        
        
      

    

and then we need to implement IUserStore, IUserPasswordStore and IUserSecurityStampStore,

public class MyUserStore : IUserStore<ApplicationUser>, IUserPasswordStore<ApplicationUser>, IUserSecurityStampStore<ApplicationUser>
{
    UserStore<IdentityUser> userStore = new UserStore<IdentityUser>(new ApplicationDbContext());
    public MyUserStore()
    {
    }
    public Task CreateAsync(ApplicationUser user)
    {
        var context = userStore.Context as ApplicationDbContext;
        context.Users.Add(user);
        context.Configuration.ValidateOnSaveEnabled = false;
        return context.SaveChangesAsync();
    }
    public Task DeleteAsync(ApplicationUser user)
    {
        var context = userStore.Context as ApplicationDbContext;
        context.Users.Remove(user);
        context.Configuration.ValidateOnSaveEnabled = false;
        return context.SaveChangesAsync();
    }
    public Task<ApplicationUser> FindByIdAsync(string userId)
    {
        var context = userStore.Context as ApplicationDbContext;
        return context.Users.Where(u => u.Id.ToLower() == userId.ToLower()).FirstOrDefaultAsync();
    }
    public Task<ApplicationUser> FindByNameAsync(string userName)
    {
        var context = userStore.Context as ApplicationDbContext;
        return context.Users.Where(u => u.UserName.ToLower() == userName.ToLower()).FirstOrDefaultAsync();
    }
    public Task UpdateAsync(ApplicationUser user)
    {
        var context = userStore.Context as ApplicationDbContext;
        context.Users.Attach(user);
        context.Entry(user).State = EntityState.Modified;
        context.Configuration.ValidateOnSaveEnabled = false;
        return context.SaveChangesAsync();
    }
    public void Dispose()
    {
        userStore.Dispose();
    }

    public Task<string> GetPasswordHashAsync(ApplicationUser user)
    {
        var identityUser = ToIdentityUser(user);
        var task = userStore.GetPasswordHashAsync(identityUser);
        SetApplicationUser(user, identityUser);
        return task;
    }
    public Task<bool> HasPasswordAsync(ApplicationUser user)
    {
        var identityUser = ToIdentityUser(user);
        var task = userStore.HasPasswordAsync(identityUser);
        SetApplicationUser(user, identityUser);
        return task;
    }
    public Task SetPasswordHashAsync(ApplicationUser user, string passwordHash)
    {
        var identityUser = ToIdentityUser(user);
        var task = userStore.SetPasswordHashAsync(identityUser, passwordHash);
        SetApplicationUser(user, identityUser);
        return task;
    }
    public Task<string> GetSecurityStampAsync(ApplicationUser user)
    {
        var identityUser = ToIdentityUser(user);
        var task = userStore.GetSecurityStampAsync(identityUser);
        SetApplicationUser(user, identityUser);
        return task;
    }
    public Task SetSecurityStampAsync(ApplicationUser user, string stamp)
    {
        var identityUser = ToIdentityUser(user);
        var task = userStore.SetSecurityStampAsync(identityUser, stamp);
        SetApplicationUser(user, identityUser);
        return task;
    }
    private static void SetApplicationUser(ApplicationUser user, IdentityUser identityUser)
    {
        user.PasswordHash = identityUser.PasswordHash;
        user.SecurityStamp = identityUser.SecurityStamp;
        user.Id = identityUser.Id;
        user.UserName = identityUser.UserName;
    }
    private IdentityUser ToIdentityUser(ApplicationUser user)
    {
        return new IdentityUser
        {
            Id = user.Id,
            PasswordHash = user.PasswordHash,
            SecurityStamp = user.SecurityStamp,
            UserName = user.UserName
        };
    }
}

      

        
        
        
      

    

For the password hash and security stamp, I am using the UserStore implementation to simplify the process. Finally, we just need to change the constructor of the AccountController to use our MyUserStore implementation,

public AccountController()
    : this(new UserManager<ApplicationUser>(new MyUserStore()))
{
}

public AccountController(UserManager<ApplicationUser> userManager)
{
    UserManager = userManager;
}

      

        
        
        
      

    

To remove unnecessary columns in the Users table. You can try something like this

public partial class ModifyUser: DbMigration
{
    public override void Up()
    {
        AddColumn("dbo.AspNetUsers", "NewField", c => c.String());
    }

    public override void Down()
    {
        DropColumn("dbo.AspNetUsers", "NewColumn");
    }
}

      

        
        
        
      

    

Then in packageManager run PM> update-database