Allow setting arbitrary headers in API client

api/api.go

@@ -314,6 +314,8 @@ type Config struct {
 	Namespace string
 
 	TLSConfig TLSConfig
+
+	Headers map[string]string
 }
 
 // TLSConfig is used to generate a TLSClientConfig that's useful for talking to
@@ -855,6 +857,10 @@ func (c *Client) newRequest(method, path string) *request {
 		params: make(map[string][]string),
 		header: make(http.Header),
 	}
+
+	for k, v := range c.config.Headers {
+		r.header.Set(k, v)
+	}
 	if c.config.Datacenter != "" {
 		r.params.Set("dc", c.config.Datacenter)
 	}

api/api_test.go

@@ -808,6 +808,22 @@ func TestAPI_SetWriteOptions(t *testing.T) {
 	}
 }
 
+func TestAPI_Headers(t *testing.T) {
+	t.Parallel()
+	c, s := makeClientWithConfig(t, func(c *Config) {
+		c.Headers = map[string]string{
+			"Hello": "World",
+		}
+	}, nil)
+	defer s.Stop()
+
+	r := c.newRequest("GET", "/v1/kv/foo")
+
+	if r.header.Get("Hello") != "World" {
+		t.Fatalf("bad: %v", r.header)
+	}
+}
+
 func TestAPI_RequestToHTTP(t *testing.T) {
 	t.Parallel()
 	c, s := makeClient(t)