Container issue: Authentication and authorization for SPAs

23K PV

This is the Container issue for this doc. Reopen each issue you are working on so the owner is notified.

PU issue
- [ ] Token expiration #12727
- [ ] How to extend the user registration UI? #12552
- [ ] Alternatives for non-SPA login/signup pages #16493
- [ ] Improve Docs about identity server #17798
- [ ] More detail to "ApplicationDbContext" #18077
- [ ] I don't understand the value proposition of IdentityServer in an SPA scenario #18524
- [ ] Details about reconfiguring existing API resources and clients #18465
- [ ] Page is not current with latest changes #18478
- [ ] Example configuration for File type token signing cert. #22506
- [ ] Include Aspnet User Claims in Jwt token #22904

Not PU:
- [ ] Example: Deploy to Azure Websites Linux Support? #16392
- [ ] The description of the IdentityServer json is in reversed order #16768
- [ ] Documentation not up to date for .Net Core 3.1 Identity #18766
- [ ]
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#### Document Details

⚠ *Do not edit this section. It is required for docs.microsoft.com ➟ GitHub issue linking.*

* ID: 21cb7455-3305-9316-5440-bdc22947a82d
* Version Independent ID: 137d4b94-7b26-3911-b22d-42c754a95fc1
* Content: [Introduction to authentication for Single Page Apps on ASP.NET Core](https://docs.microsoft.com/en-us/aspnet/core/security/authentication/identity-api-authorization?view=aspnetcore-3.0#feedback)
* Content Source: [aspnetcore/security/authentication/identity-api-authorization.md](https://github.com/aspnet/AspNetCore.Docs/blob/master/aspnetcore/security/authentication/identity-api-authorization.md)
* Product: **aspnet-core**
* Technology: **aspnetcore-security**
* GitHub Login: @javiercn
* Microsoft Alias: **scaddie**