Misc updates for the JWT sample application

[Shane32]

• Pull TokenValidationParameters from the call to AddJwtBearer so that the reference to the static property JwtHelper.Instance is not necessary
• Eliminate the static property JwtHelper.Instance
• Reconfigure Program.cs to use a local variable instead of a static property
• Reconfigure OAuthController to pull JwtHelper from DI
• Add the 'iat' claim to generated tokens (required for Open ID Connect)
• Bump Microsoft.AspNetCore.Authentication.JwtBearer since the project is a .NET 7 sample

[codecov-commenter]

Codecov Report

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[Shane32]

As a side note, I would prefer to add another nuget package for JWT handling to this repository, specifically for the IWebSocketAuthenticationService implementation (which does not require JwtHelper to be useful). I cannot put it in the main package because it requires another dependency. However, this makes an assumption about the format of the websocket initialization packet payload, which may be different from user to user as there is no official standard. It also only works for JWT, and not any other authentication mechanism. So as of now I think we should just leave it as a sample application. I plan to keep this sample code up to date as best I can so users may copy it if they wish into their own application.

[sungam3r]

No TokenValidationResult anymore? Does ValidateToken throw in case of any error?

[Shane32]

Correct; it throws in the case that the token is invalid for any reason (according to the parameters defined in tokenValidationParameters). So for example, if TokenValidationParameters.ValidateIssuer is true, then the issuer must match or an exception is thrown.