Make ApiSecret a required property

src/Passwordless/PasswordlessOptions.cs

@@ -21,7 +21,7 @@ public class PasswordlessOptions
     /// <summary>
     /// Gets or sets the secret API key used to authenticate with the Passwordless API.
     /// </summary>
-    public string ApiSecret { get; set; } = default!;
+    public required string ApiSecret { get; set; }
 
     /// <summary>
     /// Gets or sets the public API key used to interact with the Passwordless API.

src/Passwordless/Polyfill.CompilerServices.cs

@@ -0,0 +1,36 @@
+namespace System.Runtime.CompilerServices;
+
+#if !NET5_0_OR_GREATER
+// https://learn.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.isexternalinit
+internal static class IsExternalInit { }
+#endif
+
+#if !NET7_0_OR_GREATER
+// https://learn.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.requiredmemberattribute
+[AttributeUsage(
+    AttributeTargets.Class
+    | AttributeTargets.Field
+    | AttributeTargets.Property
+    | AttributeTargets.Struct,
+    Inherited = false
+)]
+internal class RequiredMemberAttribute : Attribute { }
+
+// https://learn.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.compilerfeaturerequiredattribute
+[AttributeUsage(AttributeTargets.All, AllowMultiple = true, Inherited = false)]
+internal partial class CompilerFeatureRequiredAttribute : Attribute
+{
+    public string FeatureName { get; }
+
+    public bool IsOptional { get; init; }
+
+    public CompilerFeatureRequiredAttribute(string featureName) => FeatureName = featureName;
+}
+
+internal partial class CompilerFeatureRequiredAttribute
+{
+    public const string RefStructs = nameof(RefStructs);
+
+    public const string RequiredMembers = nameof(RequiredMembers);
+}
+#endif