Add UserClaims enricher to log authenticated user claim values

[Copilot]

Summary

This PR implements a new UserClaimsEnricher for Serilog that allows logging of specific user claim values from authenticated users. This enhancement provides better traceability by capturing relevant user-specific information in logs.

Changes

New Enricher

• UserClaimsEnricher: A new enricher that logs configurable user claim values
  • Accepts a list of claim names to log via params string[] claimNames
  • Only enriches logs when the user is authenticated
  • Handles missing claims gracefully by logging null values instead of throwing errors or skipping
  • Caches claim values in HttpContext.Items for optimal performance

Extension Method

• Added WithUserClaims() extension method to ClientInfoLoggerConfigurationExtensions
• Supports both programmatic configuration and appsettings.json configuration

Usage Examples

Programmatic configuration:

using System.Security.Claims;

Log.Logger = new LoggerConfiguration()
    .Enrich.WithUserClaims(ClaimTypes.NameIdentifier, ClaimTypes.Email)
    .WriteTo.Console()
    .CreateLogger();

Configuration via appsettings.json:

{
  "Serilog": {
    "Using": ["Serilog.Enrichers.ClientInfo"],
    "Enrich": [
      {
        "Name": "WithUserClaims",
        "Args": {
          "claimNames": [
            "http://schemas.xmlsoap.org/ws/2005/05/identity/claims/nameidentifier",
            "http://schemas.xmlsoap.org/ws/2005/05/identity/claims/emailaddress"
          ]
        }
      }
    ]
  }
}

Features

✅ Configurable Claims: Specify which claims to log by passing claim names as parameters
✅ Null-Safe: Missing claims are logged as null rather than causing errors
✅ Authentication-Aware: Only enriches logs for authenticated users
✅ Performance Optimized: Claims are cached per request to avoid redundant lookups
✅ Consistent API: Follows the same patterns as existing enrichers in the library

Testing

Added comprehensive test coverage with 10 new test cases covering:

• Authenticated users with valid claims
• Missing claims (null value handling)
• Unauthenticated users (no enrichment)
• Null HttpContext handling
• Multiple claims
• Custom claim types
• Caching behavior
• Empty claim arrays

All 55 tests pass (45 existing + 10 new).

Documentation

Updated README.md with:

• UserClaims section with detailed examples
• Code examples for both C# and JSON configuration
• Feature descriptions and behavior documentation

Fixes #[issue_number]

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Implement Enricher to Log User Claims</issue_title>
<issue_description>Implement a new enricher for Serilog that logs user claims. The enricher should:

• Accept a configurable list of claim names to log.
• If the user is authenticated, log the values of the specified claims.
• If a claim value is null, log it as null (do not skip or throw an error).

This will enhance client information logging by capturing relevant claim values for authenticated users.</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #62

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