Support RFC 7807 error handling.

[daigok]

Is your feature request related to a problem? Please describe.
Not relate to a problem.

Describe the solution you'd like
Current error handling is slightly difference from RFC 7807 style. I think it would be better to support standard specification rather than the arbitrary one.

Describe alternatives you've considered
If I customize HTTPException error handling, I can change the response style to follow RFC 7807.

Additional context
Please add RFC 7807 related attributes to HTTPException and also change the response format to follow the specification.

[tiangolo]

I see the main change to make it conformant would be to return validation errors in something different than details.

But then the type URL would have to be something probably application-specific, we could generate a default title and detail saying that there was an error, but I'm not sure how useful that would be, taking into account that suddenly all the validation errors would no longer be in details but in some other key, and that there would be some extra keys.

I imagine that could break a bunch of applications...

On the other side, I can see this could be easily implemented in application-specific code, overriding the current validation handlers and returning a custom response: https://fastapi.tiangolo.com/tutorial/handling-errors/#override-the-httpexception-error-handler

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[fbidu]

@tiangolo I was reading through RFC 7807 recently and I'm planning on implementing it in Python to get a feel of how it would work in practice. If you think that it has some place in FastAPI as a plugin, an extension or something like that, I'd be glad to contribute here!

[tiangolo]

Thanks @fbidu ! In FastAPI the main change would be to move detail to be a str description of the error and add another field with the structured error object, maybe some data or similar.

I haven't wanted to do it as it would break backwards compatibility, but maybe in the future, I end up doing it 🤷 🤓

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