Add reset password support to identity endpoints

[halter73]

Background and Motivation

Add email confirmation and reset password support to identity endpoints.

Proposed API

// Microsoft.Extensions.Identity.Core.dll

// This namespace and interface already exist in Microsoft.AspNetCore.Identity.UI.dll
// but is new in Microsoft.Extensions.Identity.Core.dll
+ namespace Microsoft.AspNetCore.Identity.UI.Services;

+ public interface IEmailSender
+ {
+    Task SendEmailAsync(string email, string subject, string htmlMessage);
+ }

// Used so that Identity UI's unconfigured email sender logic works the same way regardless of whether
// it was added by AddApiEndpoints or AddDefaultUI
+ public sealed class NoOpEmailSender : IEmailSender
+ {
+    public Task SendEmailAsync(string email, string subject, string htmlMessage) => Task.CompletedTask;
+ }

// Microsoft.AspNetCore.Identity.UI.dll
+ [assembly: TypeForwardedTo(typeof(IEmailSender))]

Usage Examples

https://www.twilio.com/blog/how-to-send-asp-net-core-identity-emails-with-twilio-sendgrid

Alternative Designs

Create a new duplicate interface in a better namespace like just Microsoft.AspNetCore.Identity. Possibly use different methods for different kind of emails. E.g. SendConfirmationEmail, SendPasswordResetEmail, etc... Maybe this could be parameterized by TUser.

Risks

If people wanted to use Identity UI and Identity API endpoints in the same app with different email senders. This could make that hard or impossible to do.

[ghost]

Thank you for submitting this for API review. This will be reviewed by @dotnet/aspnet-api-review at the next meeting of the ASP.NET Core API Review group. Please ensure you take a look at the API review process documentation and ensure that:

• The PR contains changes to the reference-assembly that describe the API change. Or, you have included a snippet of reference-assembly-style code that illustrates the API change.
• The PR describes the impact to users, both positive (useful new APIs) and negative (breaking changes).
• Someone is assigned to "champion" this change in the meeting, and they understand the impact and design of the change.

[halter73]

API Review Notes:

• Can the string htmlMessage be null or empty?
  • Sure, but we can promise to always send a non-null string. We'll make it "" if we want empty.
• What do we think about NoOp in the name?
  • https://source.dot.net/#Microsoft.AspNetCore.Authentication.Core/NoopClaimsTransformation.cs,6320ffc78137554d is the only other example we could find that references "noop" and it's capitalized differently.
• Will the TypeForwardedTo cause problems since it's in a package and referencing a type now in the shared framework?
  • It could cause compilation issues due to two types with the same name in different assemblies, but we think this is okay. If you're recompiling, update the shared runtime.

API Approved!

// Microsoft.Extensions.Identity.Core.dll
+ namespace Microsoft.AspNetCore.Identity.UI.Services;

+ public interface IEmailSender
+ {
+    Task SendEmailAsync(string email, string subject, string htmlMessage);
+ }

+ public sealed class NoopEmailSender : IEmailSender
+ {
+    public Task SendEmailAsync(string email, string subject, string htmlMessage) => Task.CompletedTask;
+ }

// Microsoft.AspNetCore.Identity.UI.dll
+ [assembly: TypeForwardedTo(typeof(IEmailSender))]