diff --git a/Tiku.Api/Configuration/NetworkConfigurationExtensions.cs b/Tiku.Api/Configuration/NetworkConfigurationExtensions.cs
index 9b80239..2361ee4 100644
--- a/Tiku.Api/Configuration/NetworkConfigurationExtensions.cs
+++ b/Tiku.Api/Configuration/NetworkConfigurationExtensions.cs
@@ -60,8 +60,9 @@ internal static class NetworkConfigurationExtensions
                                      options.OwnerActivationUrlTemplate.Replace("{host}", "tenant.example.com", StringComparison.Ordinal),
                                      UriKind.Absolute,
                                      out var activationOrigin) &&
-                                 (activationOrigin.Scheme == Uri.UriSchemeHttp || activationOrigin.Scheme == Uri.UriSchemeHttps),
-                "Tenant provisioning requires a default offering code, valid trial/activation durations, and an absolute HTTP(S) owner activation URL template containing {host}.")
+                                 activationOrigin.Scheme == Uri.UriSchemeHttps &&
+                                 ValidateDevelopmentActivationTemplate(options, environment.IsDevelopment()),
+                "Tenant provisioning requires a default offering code, valid trial/activation durations, an HTTPS owner activation URL template, and permits an HTTP template only for Development .localhost sites.")
             .ValidateOnStart();
         if (environment.IsProduction())
         {
@@ -107,4 +108,24 @@ internal static class NetworkConfigurationExtensions
 
         return services;
     }
+
+    private static bool ValidateDevelopmentActivationTemplate(
+        TenantProvisioningOptions options,
+        bool isDevelopment)
+    {
+        if (string.IsNullOrWhiteSpace(options.DevelopmentLocalhostOwnerActivationUrlTemplate))
+        {
+            return true;
+        }
+
+        return isDevelopment &&
+               options.DevelopmentLocalhostOwnerActivationUrlTemplate.Contains("{host}", StringComparison.Ordinal) &&
+               Uri.TryCreate(
+                   options.DevelopmentLocalhostOwnerActivationUrlTemplate.Replace(
+                       "{host}", "tenant.localhost", StringComparison.Ordinal),
+                   UriKind.Absolute,
+                   out var developmentOrigin) &&
+               (developmentOrigin.Scheme == Uri.UriSchemeHttp ||
+                developmentOrigin.Scheme == Uri.UriSchemeHttps);
+    }
 }
diff --git a/Tiku.Api/appsettings.Development.json b/Tiku.Api/appsettings.Development.json
index 4f65b31..e680379 100644
--- a/Tiku.Api/appsettings.Development.json
+++ b/Tiku.Api/appsettings.Development.json
@@ -29,7 +29,7 @@
     "EnableDevelopmentLocalhostBypass": true
   },
   "TenantProvisioning": {
-    "OwnerActivationUrlTemplate": "http://{host}:5180"
+    "DevelopmentLocalhostOwnerActivationUrlTemplate": "http://{host}:5180"
   },
   "Authentication": {
     "Sms": {
diff --git a/Tiku.Application/PlatformAdmin/PlatformAdminModels.cs b/Tiku.Application/PlatformAdmin/PlatformAdminModels.cs
index e238b31..e4e91f1 100644
--- a/Tiku.Application/PlatformAdmin/PlatformAdminModels.cs
+++ b/Tiku.Application/PlatformAdmin/PlatformAdminModels.cs
@@ -139,6 +139,40 @@ public sealed class TenantProvisioningOptions
     public int DefaultTrialDays { get; set; } = 14;
     public int OwnerActivationMinutes { get; set; } = 30;
     public string OwnerActivationUrlTemplate { get; set; } = "https://{host}";
+    public string? DevelopmentLocalhostOwnerActivationUrlTemplate { get; set; }
+}
+
+public static class TenantOwnerActivationUrlPolicy
+{
+    public static string Build(
+        TenantProvisioningOptions options,
+        string host,
+        Guid activationId,
+        string token)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+        ArgumentException.ThrowIfNullOrWhiteSpace(host);
+        ArgumentException.ThrowIfNullOrWhiteSpace(token);
+
+        var normalizedHost = host.Trim().TrimEnd('.').ToLowerInvariant();
+        var useDevelopmentLocalhost = normalizedHost.EndsWith(".localhost", StringComparison.Ordinal) &&
+                                      !string.IsNullOrWhiteSpace(options.DevelopmentLocalhostOwnerActivationUrlTemplate);
+        var template = useDevelopmentLocalhost
+            ? options.DevelopmentLocalhostOwnerActivationUrlTemplate!
+            : options.OwnerActivationUrlTemplate;
+        var origin = template.Replace("{host}", normalizedHost, StringComparison.Ordinal).TrimEnd('/');
+        if (!Uri.TryCreate(origin, UriKind.Absolute, out var uri) ||
+            (!useDevelopmentLocalhost && uri.Scheme != Uri.UriSchemeHttps) ||
+            (useDevelopmentLocalhost &&
+             uri.Scheme != Uri.UriSchemeHttp &&
+             uri.Scheme != Uri.UriSchemeHttps))
+        {
+            throw new InvalidOperationException(
+                "Owner activation URLs must use HTTPS except for an explicitly configured Development .localhost origin.");
+        }
+
+        return $"{origin}/activate/{activationId}#token={token}";
+    }
 }
 
 public sealed record TenantBillingPolicyItem(
diff --git a/Tiku.Infrastructure/PlatformAdmin/PlatformAdminService.cs b/Tiku.Infrastructure/PlatformAdmin/PlatformAdminService.cs
index 191487c..3b5fd15 100644
--- a/Tiku.Infrastructure/PlatformAdmin/PlatformAdminService.cs
+++ b/Tiku.Infrastructure/PlatformAdmin/PlatformAdminService.cs
@@ -1436,12 +1436,7 @@ internal sealed class PlatformAdminService(
         Convert.ToBase64String(value).TrimEnd('=').Replace('+', '-').Replace('/', '_');
 
     private string BuildOwnerActivationUrl(string host, Guid activationId, string token)
-    {
-        var siteOrigin = provisioning.OwnerActivationUrlTemplate
-            .Replace("{host}", host, StringComparison.Ordinal)
-            .TrimEnd('/');
-        return $"{siteOrigin}/activate/{activationId}#token={token}";
-    }
+        => TenantOwnerActivationUrlPolicy.Build(provisioning, host, activationId, token);
 
     private static JsonElement JsonObjectOrDefault(JsonElement value) =>
         value.ValueKind == JsonValueKind.Object ? value.Clone() : JsonDocument.Parse("{}").RootElement.Clone();
diff --git a/Tiku.UnitTests/Tenancy/TenantOwnerActivationUrlPolicyTests.cs b/Tiku.UnitTests/Tenancy/TenantOwnerActivationUrlPolicyTests.cs
new file mode 100644
index 0000000..9011a30
--- /dev/null
+++ b/Tiku.UnitTests/Tenancy/TenantOwnerActivationUrlPolicyTests.cs
@@ -0,0 +1,48 @@
+using Tiku.Application.PlatformAdmin;
+
+namespace Tiku.UnitTests.Tenancy;
+
+public sealed class TenantOwnerActivationUrlPolicyTests
+{
+    [Fact]
+    public void Custom_domain_always_uses_secure_activation_origin()
+    {
+        var id = Guid.NewGuid();
+        var options = new TenantProvisioningOptions
+        {
+            OwnerActivationUrlTemplate = "https://{host}",
+            DevelopmentLocalhostOwnerActivationUrlTemplate = "http://{host}:5180"
+        };
+
+        var url = TenantOwnerActivationUrlPolicy.Build(options, "School.Example.Test", id, "secret");
+
+        Assert.Equal($"https://school.example.test/activate/{id}#token=secret", url);
+    }
+
+    [Fact]
+    public void Development_localhost_can_use_explicit_http_origin()
+    {
+        var id = Guid.NewGuid();
+        var options = new TenantProvisioningOptions
+        {
+            OwnerActivationUrlTemplate = "https://{host}",
+            DevelopmentLocalhostOwnerActivationUrlTemplate = "http://{host}:5180"
+        };
+
+        var url = TenantOwnerActivationUrlPolicy.Build(options, "school.localhost", id, "secret");
+
+        Assert.Equal($"http://school.localhost:5180/activate/{id}#token=secret", url);
+    }
+
+    [Fact]
+    public void Insecure_custom_domain_template_is_rejected()
+    {
+        var options = new TenantProvisioningOptions
+        {
+            OwnerActivationUrlTemplate = "http://{host}"
+        };
+
+        Assert.Throws<InvalidOperationException>(() =>
+            TenantOwnerActivationUrlPolicy.Build(options, "school.example.test", Guid.NewGuid(), "secret"));
+    }
+}