Add missing annotations

Add missing [NotNull] annotations to the Alipay and Notion handlers.

Author: martincostello

src/AspNet.Security.OAuth.Alipay/AlipayAuthenticationHandler.cs

@@ -215,7 +215,7 @@ private string GetRSA2Signature([NotNull] SortedDictionary<string, string> sorte
         }
 
          /// <inheritdoc />
-        protected override string BuildChallengeUrl(AuthenticationProperties properties, string redirectUri)
+        protected override string BuildChallengeUrl([NotNull] AuthenticationProperties properties, [NotNull] string redirectUri)
         {
             var scopeParameter = properties.GetParameter<ICollection<string>>(OAuthChallengeProperties.ScopeKey);
             var scope = scopeParameter != null ? FormatScope(scopeParameter) : FormatScope();

src/AspNet.Security.OAuth.Notion/NotionAuthenticationHandler.cs

@@ -32,7 +32,7 @@ public NotionAuthenticationHandler(
         {
         }
 
-        protected override async Task<OAuthTokenResponse> ExchangeCodeAsync(OAuthCodeExchangeContext context)
+        protected override async Task<OAuthTokenResponse> ExchangeCodeAsync([NotNull] OAuthCodeExchangeContext context)
         {
             var tokenRequestParameters = new Dictionary<string, string>()
             {