Use IValidateOptions<T> to validate the options created

src/FaluSdk/Extensions/IServiceCollectionExtensions.cs

@@ -67,7 +67,7 @@ public static IHttpClientBuilder AddFalu<TClient, TClientOptions>(this IServiceC
         }
 
         // register post configuration for validation purposes
-        services.AddSingleton<IPostConfigureOptions<TClientOptions>, PostConfigureFaluClientOptions<TClientOptions>>();
+        services.ConfigureOptions<FaluClientConfigureOptions<TClientOptions>>();
 
         // get the version from the assembly
         var productVersion = typeof(TClient).Assembly.GetName().Version!.ToString(3);

src/FaluSdk/FaluClientOptionsPostConfigureOptions.cs → src/FaluSdk/FaluClientConfigureOptions.cs

@@ -2,22 +2,30 @@
 
 namespace Falu;
 
-internal class PostConfigureFaluClientOptions<TClientOptions> : IPostConfigureOptions<TClientOptions> where TClientOptions : FaluClientOptions
+internal class FaluClientConfigureOptions<TClientOptions> : IPostConfigureOptions<TClientOptions>, IValidateOptions<TClientOptions>
+    where TClientOptions : FaluClientOptions
 {
     public void PostConfigure(string name, TClientOptions options)
+    {
+        // intentionally left blank for future use
+    }
+
+    public ValidateOptionsResult Validate(string name, TClientOptions options)
     {
         if (string.IsNullOrWhiteSpace(options.ApiKey))
         {
             var message = "Your API key is invalid, as it is an empty string. You can "
                         + "double-check your API key from the Falu Dashboard. See "
                         + "https://docs.falu.io/api/authentication for details or contact support "
                         + "at https://falu.com/support/email if you have any questions.";
-            throw new FaluException(message);
+            return ValidateOptionsResult.Fail(message);
         }
 
         if (options.Retries < 0)
         {
-            throw new FaluException("Retries cannot be negative.");
+            return ValidateOptionsResult.Fail("Retries cannot be negative.");
         }
+
+        return ValidateOptionsResult.Success;
     }
 }

tests/FaluSdk.Tests/ServiceCollectionExtensionsTests.cs

@@ -15,7 +15,7 @@ public void TestAddFaluWithoutApiKey()
         var provider = services.BuildServiceProvider();
 
         // Act && Assert
-        Assert.Throws<FaluException>(() => provider.GetRequiredService<FaluClient>());
+        Assert.Throws<OptionsValidationException>(() => provider.GetRequiredService<FaluClient>());
     }
 
     [Fact]