fix(build): Support for Custom-Header (#102) & wrap() with key version

* Support for Custom-Header

Signed-off-by: Harshit Gupta <harshitgupta@Harshits-MacBook-Pro.local>
Signed-off-by: Harshit Gupta <harshitgupta@harshits-mbp.in.ibm.com>

README.md

@@ -341,3 +341,34 @@ if err != nil {
 }
 fmt.Println(keys)
 ```
+
+### Support for Adding Custom Header
+
+
+1) From ServiceClient (For Every API Call)
+```go
+cc := kp.ClientConfig{
+    BaseURL:    "BASE_URL",
+    APIKey:     "API_KEY",
+    InstanceID: "INSTANCE_ID",
+    Headers: http.Header{
+      "Custom-Header":  {"Custom-Value"},
+    },
+  }
+```
+
+2) From ServiceCall (Per API Call)
+
+* Define Header just before the API Call and Empty out when done.
+
+```go
+client.Config.Headers = make(http.Header))
+client.Config.Headers.Set("Custom-Header", "Custom-Header-Value")
+
+key, err := client.CreateKey(params)
+  if err != nil {
+    panic(err)
+  }
+
+client.Config.Headers = http.Header{}
+```

kp.go

@@ -71,13 +71,14 @@ type ctxKey string
 // ClientConfig ...
 type ClientConfig struct {
 	BaseURL       string
-	Authorization string  // The IBM Cloud (Bluemix) access token
-	APIKey        string  // Service ID API key, can be used instead of an access token
-	TokenURL      string  // The URL used to get an access token from the API key
-	InstanceID    string  // The IBM Cloud (Bluemix) instance ID that identifies your Key Protect service instance.
-	KeyRing       string  // The ID of the target Key Ring the key is associated with. It is optional but recommended for better performance.
-	Verbose       int     // See verbose values above
-	Timeout       float64 // KP request timeout in seconds.
+	Authorization string      // The IBM Cloud (Bluemix) access token
+	APIKey        string      // Service ID API key, can be used instead of an access token
+	TokenURL      string      // The URL used to get an access token from the API key
+	InstanceID    string      // The IBM Cloud (Bluemix) instance ID that identifies your Key Protect service instance.
+	KeyRing       string      // The ID of the target Key Ring the key is associated with. It is optional but recommended for better performance.
+	Verbose       int         // See verbose values above
+	Timeout       float64     // KP request timeout in seconds.
+	Headers       http.Header // Support for Custom Header
 }
 
 // DefaultTransport ...
@@ -255,6 +256,12 @@ func (c *Client) do(ctx context.Context, req *http.Request, res interface{}) (*h
 	if c.Config.KeyRing != "" {
 		req.Header.Set("x-kms-key-ring", c.Config.KeyRing)
 	}
+	// Adding check for Custom Header Input
+	if c.Config.Headers != nil {
+		for key, value := range c.Config.Headers {
+			req.Header.Set(key, strings.Join(value, ","))
+		}
+	}
 
 	// set request up to be retryable on 500-level http codes and client errors
 	retryableClient := getRetryableClient(&c.HttpClient)