ASP.NET Core 2.1 Identity: How to remove the Default UI razor pages?

I upvoted the first answer because it got me 90 percent there, wanted to give out the rest (it was a little too long to put in the comments). So you'll want to keep that /Areas/Identity/ folder because it points to your shared folder if you happen to be using the header from the default template, if not it doesn't matter, delete it. The backend will still point to Identity/Account/Register/, so create a controller called Account make a folder in views called Account and put the Register.cshtml. I took the original html from a debugger window that you can use as a template to customize. Put inside Register.cshtml:

<div class="container body-content">


<h2>Register</h2>

<div class="row">
    <div class="col-md-4">
        <form method="post" action="/Identity/Account/Register" novalidate="novalidate">
            <h4>Create a new account.</h4>
            <hr>
            <div class="text-danger validation-summary-valid" data-valmsg-summary="true"><ul><li style="display:none"></li>
</ul></div>
            <div class="form-group">
                <label for="Input_Email">Email</label>
                <input class="form-control" type="email" data-val="true" data-val-email="The Email field is not a valid e-mail address." data-val-required="The Email field is required." id="Input_Email" name="Input.Email" value="">
                <span class="text-danger field-validation-valid" data-valmsg-for="Input.Email" data-valmsg-replace="true"></span>
            </div>
            <div class="form-group">
                <label for="Input_Password">Password</label>
                <input class="form-control" type="password" data-val="true" data-val-length="The Password must be at least 6 and at max 100 characters long." data-val-length-max="100" data-val-length-min="6" data-val-required="The Password field is required." id="Input_Password" name="Input.Password">
                <span class="text-danger field-validation-valid" data-valmsg-for="Input.Password" data-valmsg-replace="true"></span>
            </div>
            <div class="form-group">
                <label for="Input_ConfirmPassword">Confirm password</label>
                <input class="form-control" type="password" data-val="true" data-val-equalto="The password and confirmation password do not match." data-val-equalto-other="*.Password" id="Input_ConfirmPassword" name="Input.ConfirmPassword">
                <span class="text-danger field-validation-valid" data-valmsg-for="Input.ConfirmPassword" data-valmsg-replace="true"></span>
            </div>
            <button type="submit" class="btn btn-default">Register</button>
        <input name="__RequestVerificationToken" type="hidden" value="CfDJ8IWbPHM_NTJDv_7HGewWzbbRveP09yQOznYdTWL2aN5X_4_eVbNE1w8D_qz7zegloVtdAhuVOJbJLQo0ja73FB3PgYycyGpn-DfX3fJqv4Cx8ns6Ygh6M7nMxV0eozO7hoDxUfPwrIJb2RcFtyzhPpMevZ4P0M8aVyBP55SP-5C4l23dCtDXXUOAY_YLwt67dw"></form>
    </div>
</div>


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        <footer>
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        </footer>
    </div> 

Like the other answer says, alter Startup:

services.AddIdentity<IdentityUser, IdentityRole>(options => options.Stores.MaxLengthForKeys = 128)
    .AddEntityFrameworkStores<ApplicationDbContext>()
    // .AddDefaultUI()
    .AddDefaultTokenProviders();

Also gotta make the route to your controller, same Startup.cs file, keep the other route that's in there, probably keep it first now that I think about it, since it checks them sequentially:

app.UseMvc(routes =>
        {
            routes.MapRoute(
                name: "identity",
                template: "Identity/{controller=Account}/{action=Register}/{id?}");

A little late, but there is a much easier way to do it. You can add new scaffolding to override everything. Check out this article.

Using the article linked by Panagiotis Kanavos, I was able to reach a solution.

From the ASP.NET Core 2.1.0-preview1, there was a line .AddDefaultUI(), which you didn't have to include in Startup.cs.

services.AddIdentity<IdentityUser, IdentityRole>(options => options.Stores.MaxLengthForKeys = 128)
    .AddEntityFrameworkStores<ApplicationDbContext>()
    .AddDefaultUI()
    .AddDefaultTokenProviders();

In the final release version of Core 2.1 however, the same section was simplified to:

services.AddDefaultIdentity<IdentityUser>()
    .AddEntityFrameworkStores<ApplicationDbContext>();

The solution, if you change AddDefaultIdentity back to AddIdentity, you can override the defaults. I.E. don't include .AddDefaultUI() (and also don't scaffold the UI) and you can write your own.

services.AddIdentity<IdentityUser, IdentityRole>(options => options.Stores.MaxLengthForKeys = 128)
    .AddEntityFrameworkStores<ApplicationDbContext>()
    // .AddDefaultUI()
    .AddDefaultTokenProviders();

Then, I think it's safe to delete the /Areas/Identity/ folder, but I'm not 100%

Update:

I cleaned up my answer to detail the final solution I ended up going with, to remove the default identity UI razor pages that come with ASP.NET Core 2.1 and and use MVC instead.

1) In Startup.cs,

    public void ConfigureServices(IServiceCollection services)
    {
        // Unrelated stuff commented out...

        // BEGIN: Identity Setup (Overrides default identity)
        services.AddIdentity<ApplicationUser, IdentityRole>(options => options.Stores.MaxLengthForKeys = 128)
            .AddEntityFrameworkStores<ApplicationDbContext>()
            .AddDefaultTokenProviders();
        // END: Identity Setup

        services.Configure<IdentityOptions>(options =>
        {
            // Set your identity Settings here (password length, etc.)
        });

        // More unrelated stuff commented out...

        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);

        // Added after AddMvc()
        services.ConfigureApplicationCookie(options =>
        {
            options.LoginPath = $"/account/login";
            options.LogoutPath = $"/account/logout";
            options.AccessDeniedPath = $"/account/access-denied";
        });

        // More unrelated stuff commented out...
    }

And obviously, replace both ApplicationUser, and IdentityRole with your own classes if required.

2) Delete the Area folder for Identity that came default with your ASP.NET Core 2.1 project.

3) Create a new separate ASP.NET Core 2.0 project (not "2.1"), with Individual User Account authentication selected in the project creation window.

4) Copy the AccountController and ManageController, with the corresponding ViewModels and Views, from the 2.0 project to your ASP.NET Core 2.1 project.

Doing the above, I haven't run into any issues so far.