The requirements of the class to create a custom middleware are not well documented

[meziantou]

What are the exact requirements for writing a custom middleware as a class?

• A constructor with a single parameter of type RequestDelegate
• A method named Invoke or InvokeAsync
  • must return a Task?
  • must have a parameter of type HttpContext

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Document Details

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• ID: 13e2d968-17a6-1a50-53cd-1d6b9ad0276d
• Version Independent ID: cd22a135-4446-79f5-89db-b741bd44a720
• Content: Write custom ASP.NET Core middleware
• Content Source: aspnetcore/fundamentals/middleware/write.md
• Product: aspnet-core
• GitHub Login: @Rick-Anderson
• Microsoft Alias: riande

[Rick-Anderson]

I agree. That should be explained in the first section.

[APIWT]

This brings up an interesting point: Should there be an interface for implementing middleware?

[meziantou]

There is already the interface IMiddleware. But you are not required to use it.

https://docs.microsoft.com/en-us/aspnet/core/fundamentals/middleware/extensibility?view=aspnetcore-2.2

[AgentFire]

I've created a request for it: #34730

You should be inclined to use the interface, im my opinion. The old way should start to be getting deprecated.