feat: Adds support for Bearer tokens to Azure Foundry

[ycastorium]

Description

Adds support for the usage of Bearer tokens in the Azure Foundry provider

Type of Change

• Bug fix (non-breaking change fixing an issue)
• New feature (non-breaking change adding functionality)
• Breaking change (fix or feature causing existing functionality to change)
• Documentation update

Breaking Changes

Testing

• Tests pass (mix test)
• Quality checks pass (mix quality)

Checklist

• My code follows the project's style guidelines
• I have updated the documentation accordingly
• I have added tests that prove my fix/feature works
• All new and existing tests pass
• My commits follow conventional commit format
• I have NOT edited CHANGELOG.md (it is auto-generated by git_ops)

Related Issues

Closes #337

[mikehostetler]

Thanks for this PR! The implementation looks good overall. I've reviewed it and have a few suggestions before merging:

Security Fix Needed

The resolve_api_key/3 function logs the first 8 characters of the API key (line 809):

Logger.debug(
  "[Azure resolve_api_key] model_family=#{model_family}, source=#{source}, key_prefix=#{if api_key, do: String.slice(api_key, 0, 8), else: "nil"}..."
)

For Bearer tokens, this leaks JWT content. Please change to:

auth_mode =
  if api_key && String.starts_with?(api_key, "Bearer "), do: "bearer", else: "api_key"

Logger.debug(
  "[Azure resolve_api_key] model_family=#{model_family}, source=#{source}, auth_mode=#{auth_mode}, key_present=#{not is_nil(api_key)}"
)

Edge Case Validation

The build_auth_header/2 function should validate Bearer tokens:

defp build_auth_header("Bearer " <> token, _model_family) do
  token = String.trim(token)

  cond do
    token == "" ->
      raise ReqLLM.Error.Invalid.Parameter.exception(
              parameter: ":api_key - Bearer token cannot be empty"
            )

    String.contains?(token, ["\r", "\n"]) ->
      raise ReqLLM.Error.Invalid.Parameter.exception(
              parameter: ":api_key - Bearer token contains invalid characters"
            )

    true ->
      {"authorization", "Bearer #{token}"}
  end
end

Additional Tests

Please add tests for these edge cases:

• Empty Bearer token ("Bearer ")
• Bearer token with only whitespace ("Bearer ")
• Bearer token with newline characters (header injection protection)

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Alternatively, please enable "Allow edits from maintainers" on this PR and I can push these fixes directly.