Add ChangeEmailAsync function

src/Auth/Requests/UpdateAccount.cs

@@ -2,6 +2,8 @@
 {
     public class UpdateAccountRequest : IdTokenRequest
     {
+        public string Email { get; set; }
+
         public string Password { get; set; }
 
         public bool ReturnSecureToken { get; set; }

src/Auth/User.cs

@@ -91,6 +91,31 @@ public async Task DeleteAsync()
             this.config.UserManager.DeleteExistingUser(this.Uid);
         }
 
+        /// <summary>
+        /// Change user's Email address.
+        /// </summary>
+        /// <param name="email"> The new Email address. </param>
+        public async Task ChangeEmailAsync(string email)
+        {
+            var token = await this.GetIdTokenAsync().ConfigureAwait(false);
+            var result = await this.updateAccount.ExecuteAsync(new UpdateAccountRequest 
+            { 
+                IdToken = token,
+                Email = email,
+                ReturnSecureToken = true
+            }).ConfigureAwait(false);
+
+            this.Credential = new FirebaseCredential
+            {
+                ExpiresIn = result.ExpiresIn,
+                IdToken = result.IdToken,
+                ProviderType = this.Credential.ProviderType,
+                RefreshToken = result.RefreshToken
+            };
+
+            this.config.UserManager.UpdateExistingUser(this);
+        }
+
         /// <summary>
         /// Change user's password.
         /// </summary>