🔧 Changes

This PR fixes multiple issues related to HTTP headers and request options in the SDK:

User-Agent Header

• Changed: Management client now uses internal.UserAgentTransport() to set User-Agent header via transport wrapper
• Fixed: User-Agent now correctly shows as Go-Auth0/v2.0.0 instead of Go-http-client/1.1
• Why: Transport wrappers ensure headers are set reliably at the transport layer, preventing them from being overwritten

Auth0-Client Header

• Changed: Management client now uses internal.Auth0ClientInfoTransport() for Auth0-Client header
• Why: Using transport wrapper instead of WithHTTPHeader ensures the header cannot be accidentally overwritten by user options

Request Options - Merging Behavior

• Fixed: HTTPHeaderOption now merges headers instead of replacing the entire header map
• Fixed: BodyPropertiesOption now merges properties instead of replacing
• Fixed: QueryParametersOption now merges query parameters instead of replacing
• Why: Multiple option calls should add to each other, not overwrite. This matches the documented behavior in EXAMPLES.md

Debug Logging

• Fixed: DebugTransport now dumps request after inner transports modify it
• Why: Debug logs now show the actual headers that were sent (including User-Agent and Auth0-Client)

Code Cleanup

• Removed: Unused imports (encoding/base64, encoding/json) from management.go

📚 References

This addresses issues where:

• User-Agent header was not being set correctly in management API requests
• Debug logs showed incomplete header information
• Multiple WithHTTPHeader/WithBodyProperties/WithQueryParameters calls would overwrite instead of merge

🔬 Testing

Existing Tests: All existing tests pass

• go test ./internal/client/... -run TestDebug - ✅ Pass
• go test ./management/client/... - ✅ Pass
• make lint - ✅ Pass

Manual Testing:
Created test client with debug logging enabled and verified:

• User-Agent header shows as Go-Auth0/v2.0.0 in debug output
• Auth0-Client header is present in debug output
• Multiple option calls properly merge instead of replace

Test Scenario:

client, _ := mgmtclient.New(domain,
    option.WithDebug(true),
    option.WithInsecure(),
)
client.Clients.List(ctx, &management.ListClientsRequestParameters{})

Before: Debug log showed User-Agent: Go-http-client/1.1
After: Debug log shows User-Agent: Go-Auth0/v2.0.0

📝 Checklist

• All new/changed/fixed functionality is covered by tests (or N/A)
• I have added documentation for all new/changed functionality (or N/A)