Review proxy headers

[alukach]

We should review the recommended best-practices with regards to operating a proxy rather than a standard API.

For example:

• Forwarded request header
• Via request header
• Proxy-Authorization request header
• Proxy-Autenticate response header
• 407 Proxy Authentication Required response status

Resources:

• MDN: Proxy servers - Reverse proxies

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Current headers applied here:

Request:

stac-auth-proxy/src/stac_auth_proxy/handlers/reverse_proxy.py

Lines 33 to 35 in 22bef9e

	headers = MutableHeaders(request.headers)
	headers.setdefault("X-Forwarded-For", request.client.host)
	headers.setdefault("X-Forwarded-Host", request.url.hostname)

Response:

stac-auth-proxy/src/stac_auth_proxy/handlers/reverse_proxy.py

Line 56 in 22bef9e

rp_resp.headers["X-Upstream-Time"] = f"{proxy_time:.3f}"