Add verify webhook signature response (#117)

Author: roopakv

.gitignore

@@ -0,0 +1,2 @@
+.idea
+.vscode

example_test.go

@@ -1,6 +1,6 @@
 package paypal_test
 
-import paypal "github.com/plutov/paypal/v3"
+import "github.com/plutov/paypal/v3"
 
 func Example() {
 	// Initialize client

types.go

@@ -852,6 +852,10 @@ type (
 		BankTXNPendingURL string `json:"bank_txn_pending_url,omitempty"`
 		UserAction        string `json:"user_action,omitempty"`
 	}
+
+	VerifyWebhookResponse struct {
+		VerificationStatus string `json:"verification_status,omitempty"`
+	}
 )
 
 // Error method implementation for ErrorResponse struct

webhooks.go

@@ -0,0 +1,54 @@
+package paypal
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+)
+
+// VerifyWebhookSignature - Use this to verify the signature of a webhook recieved from paypal.
+// Endpoint: POST /v1/notifications/verify-webhook-signature
+func (c *Client) VerifyWebhookSignature(httpReq *http.Request, webhookID string) (*VerifyWebhookResponse, error) {
+	type verifyWebhookSignatureRequest struct {
+		AuthAlgo         string          `json:"auth_algo,omitempty"`
+		CertURL          string          `json:"cert_url,omitempty"`
+		TransmissionID   string          `json:"transmission_id,omitempty"`
+		TransmissionSig  string          `json:"transmission_sig,omitempty"`
+		TransmissionTime string          `json:"transmission_time,omitempty"`
+		WebhookID        string          `json:"webhook_id,omitempty"`
+		WebhookEvent     json.RawMessage `json:"webhook_event"`
+	}
+	getBody := httpReq.GetBody
+	bodyReadCloser, err := getBody()
+	if err != nil {
+		return nil, err
+	}
+	body, err := ioutil.ReadAll(bodyReadCloser)
+	if err != nil {
+		return nil, err
+	}
+
+	verifyRequest := verifyWebhookSignatureRequest{
+		AuthAlgo:         httpReq.Header.Get("PAYPAL-AUTH-ALGO"),
+		CertURL:          httpReq.Header.Get("PAYPAL-CERT-URL"),
+		TransmissionID:   httpReq.Header.Get("PAYPAL-TRANSMISSION-ID"),
+		TransmissionSig:  httpReq.Header.Get("PAYPAL-TRANSMISSION-SIG"),
+		TransmissionTime: httpReq.Header.Get("PAYPAL-TRANSMISSION-TIME"),
+		WebhookID:        webhookID,
+		WebhookEvent:     json.RawMessage(body),
+	}
+
+	response := &VerifyWebhookResponse{}
+
+	req, err := c.NewRequest("POST", fmt.Sprintf("%s%s", c.APIBase, "/v1/notifications/verify-webhook-signature"), verifyRequest)
+	if err != nil {
+		return nil, err
+	}
+
+	if err = c.SendWithAuth(req, response); err != nil {
+		return nil, err
+	}
+
+	return response, nil
+}