use identitytoolkit/v3 go client instead of makeHTTPCall (#60)

* use identitytoolkit/v3 go client instead of makeHTTPCall

* remove unnecessary if because empty values are not sent with identitytoolkit

* refactoring to avoid multiple header set

* change execute func to setHeader

* remove url from Client type, rename relayingpartyCall interface + fix providerID mistake

* change rawId value in test to 'testuid'

Author: chemidy

auth/auth.go

@@ -22,17 +22,16 @@ import (
 	"encoding/pem"
 	"errors"
 	"fmt"
-	"net/http"
 	"strings"
 
 	"firebase.google.com/go/internal"
 	"golang.org/x/net/context"
+	"google.golang.org/api/identitytoolkit/v3"
 	"google.golang.org/api/transport"
 )
 
 const firebaseAudience = "https://identitytoolkit.googleapis.com/google.identity.identitytoolkit.v1.IdentityToolkit"
 const googleCertURL = "https://www.googleapis.com/robot/v1/metadata/x509/securetoken@system.gserviceaccount.com"
-const idToolKitURL = "https://www.googleapis.com/identitytoolkit/v3/relyingparty/"
 const issuerPrefix = "https://securetoken.google.com/"
 const tokenExpSeconds = 3600
 
@@ -64,10 +63,10 @@ type Token struct {
 // by Firebase backend services.
 type Client struct {
 	hc        *internal.HTTPClient
+	is        *identitytoolkit.Service
 	ks        keySource
 	projectID string
 	snr       signer
-	url       string
 	version   string
 }
 
@@ -118,32 +117,21 @@ func NewClient(ctx context.Context, c *internal.AuthConfig) (*Client, error) {
 		return nil, err
 	}
 
+	is, err := identitytoolkit.New(hc)
+	if err != nil {
+		return nil, err
+	}
+
 	return &Client{
 		hc:        &internal.HTTPClient{Client: hc},
+		is:        is,
 		ks:        newHTTPKeySource(googleCertURL, hc),
 		projectID: c.ProjectID,
 		snr:       snr,
-		url:       idToolKitURL,
 		version:   "Go/Admin/" + c.Version,
 	}, nil
 }
 
-// Passes the request struct, returns a byte array of the json
-func (c *Client) makeHTTPCall(ctx context.Context, serviceName string, payload interface{}, result interface{}) error {
-	versionHeader := internal.WithHeader("X-Client-Version", c.version)
-	request := &internal.Request{
-		Method: http.MethodPost,
-		URL:    c.url + serviceName,
-		Body:   internal.NewJSONEntity(payload),
-		Opts:   []internal.HTTPOption{versionHeader},
-	}
-	resp, err := c.hc.Do(ctx, request)
-	if err != nil {
-		return err
-	}
-	return resp.Unmarshal(http.StatusOK, result)
-}
-
 // CustomToken creates a signed custom authentication token with the specified user ID. The resulting
 // JWT can be used in a Firebase client SDK to trigger an authentication flow. See
 // https://firebase.google.com/docs/auth/admin/create-custom-tokens#sign_in_using_custom_tokens_on_clients