Refactor: Agent Accessor Chain

[the-avid-engineer]

Arriving from the potential need to have multiple types of agents operating in a single application, I've created this simple implementation of the IAgentAccessor interface which will resolve an agent from a chain of IAgentAccessor implementations.

Example of how to use.

The top-level service provider is expected to only have a single implementation of IAgentAccessor (if you happen to supply more than one, only the last one will be used). Therefore, the AgentAccessorChain implementation has an options object AgentAccessorChainOptions which has its own, private service collection, and this implementation will use all registered implementations of IAgentAccessor.

As an example, you could use this new implementation to combine the HttpContextAgentAccessor, which requires a HTTP Context (via IHttpContextAccessor) to return an IAgent, with a custom implementation that does not require an HTTP Context to return an IAgent. This custom implementation is entirely up to you. (More implementations may or may not come in future package releases. At this time, there is only HttpContextAgentAccessor and UnknownAgentAccessor the latter of which is only appropriate for testing purposes)

serviceCollection.Configure<AgentAccessorChainOptions>(chainOptions =>
{
    // Http Context Agent Accessor
    
    chainOptions.ServiceCollection.Configure<HttpContextAgentSignatureOptions>(signatureOptions =>
    {
        signatureOptions.RedactedHeaders = new[] { "Authorization" };
    });

    chainOptions.ServiceCollection.AddHttpContextAgentAccessor();

    // My Custom Agent Accessor

    chainOptions.ServiceCollection.AddAgentAccessor<MyCustomAgentAccessor>();
});

serviceCollection.AddAgentAccessor<AgentAccessorChain>();