add: Allow auth extra_headers to be set via .env

[gkaretka]

Title

Allow auth extra_headers to be set via environment variables

Relevant issues

Related issue: https://github.com/BerriAI/litellm/issues/8085

Type

🆕 New Feature ✅ Test

Changes

Load Authorization header from environment variables when available.

[REQUIRED] Testing - Attach a screenshot of any new tests passing locally

Documents/Projects/litellm ‹main› » pytest tests/litellm/llms/bedrock/test_base_aws_llm.py       
========================================================================== test session starts ===========================================================================
platform darwin -- Python 3.11.3, pytest-7.4.4, pluggy-1.5.0
rootdir: /Users/gkaretka/Documents/Projects/litellm
plugins: ddtrace-2.19.0, anyio-4.4.0, mock-3.14.0
collected 3 items                                                                                                                                                        

tests/litellm/llms/bedrock/test_base_aws_llm.py ...     

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Name	Status	Preview	Comments	Updated (UTC)
litellm	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Apr 24, 2025 8:36am

[mrshu]

Hey @krrishdholakia, is there anything specific that would be blocking this? It would be pretty nice to have support for this in litellm.

Thanks!

[CLAassistant]

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