Allow specifying header on a per-request basis

[AdamGS]

Is your feature request related to a problem? Please describe.
I want to be able to specify headers on a per request headers, in my specific use cases those are if-none-match and if-match as different object require different handling but I can imagine it being useful for other usescases (content-type being an obvious one).

Describe the solution you'd like
have _with_headers variants for some functions that allow for specifying a second header override (in addition to the bucket level additional_headers

Describe alternatives you've considered
Another possibility is storing some closure/middleware in Bucket that will check requests on their way out and mutate them as required.

[durch]

Thanks for the request. Part of this is now covered for uploads through the current builder/header APIs, for example put_object_builder(...).with_header(...) and put_object_with_headers(...).

The remaining question is which non-upload operations still need per-request headers. You mentioned if-none-match / if-match; could you confirm which methods you need those for on current 0.37.2? For example:

• get_object
• head_object
• presigned requests
• copy/multipart operations
• something else

I’d like to avoid adding a broad header override surface without knowing the concrete operations, because request headers are part of signing behavior and provider compatibility.