Add project files

StalwartSimpleLoginMiddleware/Utilities/ApiKeyHelper.cs

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+using System.Net.Mail;
+using System.Security.Cryptography;
+using StalwartSimpleLoginMiddleware.Entities;
+using StalwartSimpleLoginMiddleware.Models;
+
+namespace StalwartSimpleLoginMiddleware.Utilities;
+
+public class ApiKeyHelper
+{
+    public static string GenerateKey()
+    {
+        var key = new byte[64];
+        using (var generator = RandomNumberGenerator.Create())
+            generator.GetBytes(key);
+        return Convert.ToBase64String(key);
+    }
+
+    public static DbApiKey CreateDbApiKey(ApiKey dbKey)
+    {
+        return new DbApiKey
+        {
+            Key = dbKey.Key,
+            OwnerName = dbKey.OwnerEmail,
+            Claims = ClaimsHelper.BuildClaims(dbKey)
+        };
+    }
+
+    public static KeyMetadata CreateKeyMetadata(ApiKey dbKey)
+    {
+        return new KeyMetadata
+        {
+            Domain = GetEmailDomain(dbKey.OwnerEmail),
+            Members = GetMembers(dbKey, false),
+            ExternalMembers = GetMembers(dbKey, true)
+        };
+    }
+
+    public static ICollection<string> GetMembers(ApiKey dbKey, bool isExternal)
+    {
+        var members = dbKey.Members.Where(m => m.IsExternal == isExternal)
+            .Select(m => m.Email);
+
+        if (!isExternal)
+        {
+            return members.Append(dbKey.OwnerEmail)
+                .ToArray();
+        }
+
+        return members.ToArray();
+    }
+
+    public static string GetEmailDomain(string email)
+    {
+        if (string.IsNullOrEmpty(email))
+        {
+            throw new ArgumentException("Email cannot be null or empty.", nameof(email));
+        }
+
+        if (MailAddress.TryCreate(email, out var address))
+        {
+            return address.Host;
+        }
+
+        throw new ArgumentException($"Invalid email format: {email}", nameof(email));
+    }
+}