Support setting HTTP response headers using some Results methods for Minimal APIs

[martincostello]

Is there an existing issue for this?

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Is your feature request related to a problem? Please describe the problem.

Using Minimal APIs with the built-in Results class' methods allows for lots of built-in functionality to perform lots of operations a developer may wish to achieve with an HTTP endpoint, but the experience isn't as good as soon as you need to set an HTTP response header.

In this scenario you're left with at least three possible choices:

1. Mix and match use of Results with the HttpResponse so you can manually set any headers in the endpoint before returning the IResult.
2. Use IResultExtensions and a custom IResult implementation to write the body and any headers, likely duplicating implementation details from the internal IResult implementations.
3. Stop using the Results class and write to the content and headers to the HttpResponse directly in the endpoint.

As an example, take an endpoint which wishes to return an HTTP 429 problem if it wishes to rate limit the client and return a Retry-After response header. The Results.Problem() can be used to return the body and set the status code, but there is no way to set the Retry-After header directly.

To achieve the desired result, you need to either mix-and-match the lower-level HttpResponse usage in the endpoint (and potentially add an extra parameter to access it) with the Results class, write a custom extension, or not use Results at all.

The code would be simpler for the developer in non-advanced cases if they could pass through a simple key-value pair of strings through the Results methods to set HTTP response headers without having to add additional complexity and/or concepts, reducing the "minimalness".

Describe the solution you'd like

Some possible solutions to this (assuming it's not do nothing as this is considered an advanced use case) could include:

1. Add a new overload or add another optional parameter to methods such as Results.Json() and Results.Problem() that accepts additional headers to set as an IDictionary<string, string>, which would then be passed through to the internals of ObjectResult for use in the ConfigureResponseHeaders(HttpContext) method.
2. Make the IResult implementations public so behaviours could be easily overridden to extend them. For the HTTP 429 example, a developer could sub-class ObjectResult.ConfigureResponseHeaders(HttpContext) to set the additional header(s) (see also Make IResult methods more testable #37502)

Additional context

No response

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[davidfowl]

Add a new overload or add another optional parameter to methods such as Results.Json() and Results.Problem() that accepts additional headers to set as an IDictionary<string, string>, which would then be passed through to the internals of ObjectResult for use in the ConfigureResponseHeaders(HttpContext) method.

Maybe 3. Action<IHeaderDictionary>?

Results.Json(product, headers => headers["Retry-After"] = ...)

[martincostello]

I also like that idea, then you wouldn't need to allocate a dictionary just to set a header.