Header propagation POC

[tracyboehrer]

The Problem

• Need to support getting headers, and additional User-Agent info, to outgoing requests.
• Microsoft.AspNetCore.HeaderPropagation will not work since the DotNet CloudAdapter uses a queue on another thread, and the AspNet functionality is in the context of a current request only.
• We also need to carry x-ms-correlation-id over (all the time)
• I didn't want to pass headers all over.

This POC

• IHeaderPropagationFilter
  • User DI'd impl that defines the list of headers and User-Agent addition
• IHeaderPropation
  • Impl in Host.AspNet to filter the incoming headers for the incoming Microsoft.AspNetCore.Http.HttpRequest
• RequestContext
  • Uses AsyncLocal to allow anything in the async call to access the filtered headers and add to HttpClient.
  • See Microsoft.Agents.Connector.RestClients.RestClientBase.GetHttpClientAsync for usage

Flow

1. Request arrives at CloudAdapter
2. Get IHeaderPropagationFilter (passed in via DI in this case)
3. Create a host specific IHeaderPropagation using that
4. If async, IHeaderPropagation pass it to the queue
5. On the queue thread, create a new RequestContext
6. Anything within the async call will be able to access RequestContext and values.