feat: [Geneva Uploader] Implement Azure Workload Identity authentication for Geneva.

[lalitb]

Core Implementation

• Added AuthMethod::WorkloadIdentity variant (geneva-uploader/src/config_service/client.rs)

  • Uses Azure Identity SDK's WorkloadIdentityCredential for token exchange
  • Automatically reads AZURE_CLIENT_ID, AZURE_TENANT_ID, and AZURE_FEDERATED_TOKEN_FILE from environment
  • Exchanges Kubernetes service account token for Azure AD access token
  • Uses /userapi endpoint (same as Managed Identity authentication)

• Token acquisition and caching

  • Implements federated token exchange flow with Azure AD
  • Generates appropriate OAuth scopes based on resource URI and Azure cloud
  • Integrates with existing token caching mechanism

Example and Documentation

• Complete working example (examples/basic_workload_identity_test.rs)

  • Demonstrates Workload Identity configuration
  • Shows environment variable setup
  • Includes sample log generation and export

• Comprehensive setup guide (examples/README.md)

  • Step-by-step AKS cluster configuration
  • User-Assigned Managed Identity creation (NOT App Registration)
  • Federated credential setup
  • Kubernetes service account and pod deployment
  • Troubleshooting guide for common issues
  • Environment variable reference

• Docker support (examples/Dockerfile)

  • Multi-stage build for optimized image size
  • Builds the workload identity example
  • Compatible with AKS (linux/amd64)

FFI Support

• Updated FFI bindings (geneva-uploader-ffi/src/lib.rs)
  • Auto-detects Workload Identity vs System MSI based on AZURE_FEDERATED_TOKEN_FILE presence
  • Maintains backward compatibility with existing authentication methods

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

❌ Patch coverage is 16.92308% with 54 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.7%. Comparing base (1ee6a9c) to head (76c9227).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...eneva/geneva-uploader/src/config_service/client.rs	11.3%	47 Missing ⚠️
...try-exporter-geneva/geneva-uploader-ffi/src/lib.rs	0.0%	5 Missing ⚠️
...etry-exporter-geneva/geneva-uploader/src/client.rs	0.0%	1 Missing ⚠️
...r-geneva/geneva-uploader/src/config_service/mod.rs	83.3%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #467     +/-   ##
=======================================
- Coverage   53.9%   53.7%   -0.3%     
=======================================
  Files         71      71             
  Lines      11220   11262     +42     
=======================================
- Hits        6057    6056      -1     
- Misses      5163    5206     +43     

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