Pass through some proxy related headers to Django for auto header-based signin

[LukasdeBoer]

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• I have read the contributing guideline and understand that I have made the correct modifications

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Description:

This is very useful for allowing users to auto-signin based on headers. Removes the run hack needed here: babybuddy/babybuddy#643 (comment).

Benefits of this PR and context:

It's very useful when people are using it as an iframe, e.g. in home assistant, you don't want to be logging in every time you're using this tool.

How Has This Been Tested?

I've tested this locally. Without setting the flags, the tool works without any change in behavior. However, by setting:

REVERSE_PROXY_AUTH=true
PROXY_HEADER=HTTP_X_REMOTE_USER

and adding

proxy_set_header X-Remote-User 'yourusername';

to the nginx default template, you can allow auto signin of this user.

Source / References:

babybuddy/babybuddy#643 (comment)

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[LinuxServer-CI]

I am a bot, here are the test results for this PR:
https://ci-tests.linuxserver.io/lspipepr/babybuddy/v2.7.0-pkg-1ca837e7-dev-8a944308d2430777db4d8737943e319199ea5703-pr-42/index.html
https://ci-tests.linuxserver.io/lspipepr/babybuddy/v2.7.0-pkg-1ca837e7-dev-8a944308d2430777db4d8737943e319199ea5703-pr-42/shellcheck-result.xml

Tag	Passed
amd64-v2.7.0-pkg-1ca837e7-dev-8a944308d2430777db4d8737943e319199ea5703-pr-42	✅
arm64v8-v2.7.0-pkg-1ca837e7-dev-8a944308d2430777db4d8737943e319199ea5703-pr-42	✅

[aptalca]

Can't you set those env vars in the docker run or compose? They do not get processed during init, just set as is.

[LukasdeBoer]

Wow... derp. I was 100% sure I tested that but without this change it just works...closing this. Apologies for wasting your time!