cache: Pass through wait query param to the cache.Get (#5203)

This adds a MaxQueryTime field to the connect ca leaf cache request type and populates it via the wait query param. The cache will then do the right thing and timeout the operation as expected if no new leaf cert is available within that time.

Fixes #4462 

The reproduction scenario in the original issue now times out appropriately.

agent/agent_endpoint.go

@@ -1335,6 +1335,7 @@ func (s *HTTPServer) AgentConnectCALeafCert(resp http.ResponseWriter, req *http.
 		return nil, nil
 	}
 	args.MinQueryIndex = qOpts.MinQueryIndex
+	args.MaxQueryTime = qOpts.MaxQueryTime
 
 	// Verify the proxy token. This will check both the local proxy token
 	// as well as the ACL if the token isn't local. The checks done in

agent/agent_endpoint_test.go

@@ -4715,6 +4715,25 @@ func TestAgentConnectCALeafCert_goodNotLocal(t *testing.T) {
 		require.Equal("HIT", resp.Header().Get("X-Cache"))
 	}
 
+	// Test Blocking - see https://github.com/hashicorp/consul/issues/4462
+	{
+		// Fetch it again
+		resp := httptest.NewRecorder()
+		blockingReq, _ := http.NewRequest("GET", fmt.Sprintf("/v1/agent/connect/ca/leaf/test?wait=125ms&index=%d", issued.ModifyIndex), nil)
+		doneCh := make(chan struct{})
+		go func() {
+			a.srv.AgentConnectCALeafCert(resp, blockingReq)
+			close(doneCh)
+		}()
+
+		select {
+		case <-time.After(500 * time.Millisecond):
+			require.FailNow("Shouldn't block for this long - not respecting wait parameter in the query")
+
+		case <-doneCh:
+		}
+	}
+
 	// Test that caching is updated in the background
 	{
 		// Set a new CA

agent/cache-types/connect_ca_leaf.go

@@ -493,6 +493,7 @@ type ConnectCALeafRequest struct {
 	Datacenter    string
 	Service       string // Service name, not ID
 	MinQueryIndex uint64
+	MaxQueryTime  time.Duration
 }
 
 func (r *ConnectCALeafRequest) CacheInfo() cache.RequestInfo {
@@ -501,5 +502,6 @@ func (r *ConnectCALeafRequest) CacheInfo() cache.RequestInfo {
 		Key:        r.Service,
 		Datacenter: r.Datacenter,
 		MinIndex:   r.MinQueryIndex,
+		Timeout:    r.MaxQueryTime,
 	}
 }