Enable entra id via env var

[jeremydvoss]

Description

Add entra id credential configuration via env var. Required for AKS attach.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[azure-sdk]

API change check

API changes are not detected in this pull request.

[Copilot]

Pull Request Overview

This PR adds support for configuring Entra ID credentials via an environment variable, which is required for AKS attach. The changes include new tests validating env var–based authentication, an updated dependency on azure-identity in setup.py, and modifications to credential initialization in the exporter.

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
sdk/monitor/azure-monitor-opentelemetry-exporter/tests/test_base_exporter.py	Added tests for environment variable credential behavior; note duplicate test case name issue.
sdk/monitor/azure-monitor-opentelemetry-exporter/setup.py	Updated dependency to include azure-identity with a TODO for version clarification.
sdk/monitor/azure-monitor-opentelemetry-exporter/azure/monitor/opentelemetry/exporter/export/_base.py	Introduced _get_authentication_credential method and adjusted credential initialization; contains a debug print statement and a type annotation inconsistency.
sdk/monitor/azure-monitor-opentelemetry-exporter/azure/monitor/opentelemetry/exporter/_constants.py	Added constant for the authentication string environment variable.
sdk/monitor/azure-monitor-opentelemetry-exporter/README.md	Updated documentation to include details on the new environment variable configuration.
sdk/monitor/azure-monitor-opentelemetry-exporter/CHANGELOG.md	Documented the addition of Entra ID credential configuration via env var.

Comments suppressed due to low confidence (1)

sdk/monitor/azure-monitor-opentelemetry-exporter/tests/test_base_exporter.py:1107

• Duplicate test method 'test_get_authentication_credential_no_aad' detected. Please rename one of the duplicate methods so both tests can run independently.

def test_get_authentication_credential_no_aad(self, mock_managed_identity):