diff --git a/docker-env2/central-node-a/appsettings.Central.json b/docker-env2/central-node-a/appsettings.Central.json
index a082186f..a5383bd0 100644
--- a/docker-env2/central-node-a/appsettings.Central.json
+++ b/docker-env2/central-node-a/appsettings.Central.json
@@ -34,7 +34,8 @@
       "JwtSigningKey": "scadabridge-env2-dev-jwt-signing-key-must-be-at-least-32-characters-long",
       "JwtExpiryMinutes": 15,
       "IdleTimeoutMinutes": 30,
-      "RequireHttpsCookie": false
+      "RequireHttpsCookie": false,
+      "CookieName": "ZB.MOM.WW.ScadaBridge.Auth.env2"
     },
     "Communication": {
       "DeploymentTimeout": "00:02:00",
diff --git a/docker-env2/central-node-b/appsettings.Central.json b/docker-env2/central-node-b/appsettings.Central.json
index 44968208..37076f67 100644
--- a/docker-env2/central-node-b/appsettings.Central.json
+++ b/docker-env2/central-node-b/appsettings.Central.json
@@ -34,7 +34,8 @@
       "JwtSigningKey": "scadabridge-env2-dev-jwt-signing-key-must-be-at-least-32-characters-long",
       "JwtExpiryMinutes": 15,
       "IdleTimeoutMinutes": 30,
-      "RequireHttpsCookie": false
+      "RequireHttpsCookie": false,
+      "CookieName": "ZB.MOM.WW.ScadaBridge.Auth.env2"
     },
     "Communication": {
       "DeploymentTimeout": "00:02:00",
diff --git a/src/ZB.MOM.WW.ScadaBridge.Security/SecurityOptions.cs b/src/ZB.MOM.WW.ScadaBridge.Security/SecurityOptions.cs
index 34c19d22..05dc9fd4 100644
--- a/src/ZB.MOM.WW.ScadaBridge.Security/SecurityOptions.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.Security/SecurityOptions.cs
@@ -44,4 +44,18 @@ public class SecurityOptions
     /// any HTTPS request but is usable over plain HTTP.
     /// </summary>
     public bool RequireHttpsCookie { get; set; } = true;
+
+    /// <summary>The canonical default authentication-cookie name (<see cref="CookieName"/>).</summary>
+    public const string DefaultCookieName = "ZB.MOM.WW.ScadaBridge.Auth";
+
+    /// <summary>
+    /// Authentication cookie name. Defaults to <see cref="DefaultCookieName"/>. Override it
+    /// (<c>ScadaBridge:Security:CookieName</c>) to give a distinct name to a deployment that
+    /// shares a hostname with another ScadaBridge environment — browser cookies are scoped by
+    /// host+path but NOT by port, so two clusters on the same host (e.g. two local Docker
+    /// stacks on <c>localhost:9000</c> and <c>localhost:9100</c>) would otherwise clobber each
+    /// other's session under a shared cookie name. A blank/whitespace value falls back to
+    /// <see cref="DefaultCookieName"/>. Changing this invalidates existing sessions on next deploy.
+    /// </summary>
+    public string CookieName { get; set; } = DefaultCookieName;
 }
diff --git a/src/ZB.MOM.WW.ScadaBridge.Security/ServiceCollectionExtensions.cs b/src/ZB.MOM.WW.ScadaBridge.Security/ServiceCollectionExtensions.cs
index 4106c1ac..bd7fbab7 100644
--- a/src/ZB.MOM.WW.ScadaBridge.Security/ServiceCollectionExtensions.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.Security/ServiceCollectionExtensions.cs
@@ -77,23 +77,23 @@ public static class ServiceCollectionExtensions
         // now enforces Server + SearchBase + ServiceAccountDn + transport at startup. The
         // JWT signing key continues to fail-fast at JwtTokenService construction.
 
-        // Register ASP.NET Core authentication with cookie scheme. The non-
-        // SecurityOptions-coupled settings (paths, cookie name) are set here; the
-        // hardened cookie defaults that depend on SecurityOptions (idle timeout,
-        // HTTPS policy) are applied via the SecurityOptions-bound PostConfigure
-        // below through ZbCookieDefaults.Apply.
+        // Register ASP.NET Core authentication with cookie scheme. Only the static
+        // SecurityOptions-independent settings (login/logout paths) are set here; the
+        // cookie NAME and the hardened defaults that depend on SecurityOptions (idle
+        // timeout, HTTPS policy) are applied via the SecurityOptions-bound PostConfigure
+        // below (cookie name through SecurityOptions.CookieName, the rest through
+        // ZbCookieDefaults.Apply).
         services.AddAuthentication(CookieAuthenticationDefaults.AuthenticationScheme)
             .AddCookie(options =>
             {
                 options.LoginPath = "/login";
                 options.LogoutPath = "/auth/logout";
-                // The cookie NAME is app-owned and not set by ZbCookieDefaults.Apply
-                // (so co-hosted ZB apps do not clobber each other's session). Keep
-                // ScadaBridge's existing name so live sessions survive this change.
-                options.Cookie.Name = "ZB.MOM.WW.ScadaBridge.Auth";
-                // HttpOnly / SameSite / SecurePolicy / SlidingExpiration /
-                // ExpireTimeSpan are all set by ZbCookieDefaults.Apply in the
-                // SecurityOptions-bound PostConfigure below.
+                // Cookie.Name is app-owned (not set by ZbCookieDefaults.Apply, so co-hosted
+                // ZB apps do not clobber each other) AND now config-driven — it is set from
+                // SecurityOptions.CookieName in the PostConfigure below so two ScadaBridge
+                // environments sharing a hostname can be given distinct names. HttpOnly /
+                // SameSite / SecurePolicy / SlidingExpiration / ExpireTimeSpan are likewise
+                // applied there via ZbCookieDefaults.Apply.
             });
 
         // CentralUI-005: configure the cookie session as a sliding window so the
@@ -124,6 +124,15 @@ public static class ServiceCollectionExtensions
                     requireHttps: securityOptions.Value.RequireHttpsCookie,
                     idleTimeout: TimeSpan.FromMinutes(securityOptions.Value.IdleTimeoutMinutes));
 
+                // App-owned, config-driven cookie name (ScadaBridge:Security:CookieName).
+                // ZbCookieDefaults.Apply intentionally leaves the name untouched. A
+                // blank/whitespace value falls back to the canonical default so a
+                // misconfiguration cannot produce an unnamed cookie.
+                var cookieName = securityOptions.Value.CookieName;
+                cookieOptions.Cookie.Name = string.IsNullOrWhiteSpace(cookieName)
+                    ? SecurityOptions.DefaultCookieName
+                    : cookieName;
+
                 // Security-021: when the operator opts out of HTTPS-only cookies,
                 // log a Warning so an HTTP-only deployment is at least audible in
                 // the startup log. The cookie carries the embedded JWT bearer
diff --git a/tests/ZB.MOM.WW.ScadaBridge.Security.Tests/SecurityTests.cs b/tests/ZB.MOM.WW.ScadaBridge.Security.Tests/SecurityTests.cs
index d4e305a7..72037388 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.Security.Tests/SecurityTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.Security.Tests/SecurityTests.cs
@@ -515,6 +515,72 @@ public class SecurityReviewRegressionTests
         Assert.True(cookieOptions.SlidingExpiration);
     }
 
+    // --- Configurable cookie name: two ScadaBridge environments sharing a hostname
+    //     (browser cookies are scoped by host+path, NOT port) must be able to use
+    //     distinct cookie names so signing into one does not clobber the other's session. ---
+
+    [Fact]
+    public void AddSecurity_AuthCookie_DefaultsToCanonicalName()
+    {
+        var services = new ServiceCollection();
+        services.AddLogging();
+        services.AddDataProtection();
+        services.AddSecurity();
+
+        using var provider = services.BuildServiceProvider();
+        var cookieOptions = provider
+            .GetRequiredService<IOptionsMonitor<Microsoft.AspNetCore.Authentication.Cookies.CookieAuthenticationOptions>>()
+            .Get(Microsoft.AspNetCore.Authentication.Cookies.CookieAuthenticationDefaults.AuthenticationScheme);
+
+        // Unconfigured deployments (incl. production and the primary docker cluster) keep the
+        // canonical name, so existing sessions survive and only an explicit override diverges.
+        Assert.Equal(SecurityOptions.DefaultCookieName, cookieOptions.Cookie.Name);
+        Assert.Equal("ZB.MOM.WW.ScadaBridge.Auth", cookieOptions.Cookie.Name);
+    }
+
+    [Fact]
+    public void AddSecurity_AuthCookie_CookieNameIsConfigurable()
+    {
+        var services = new ServiceCollection();
+        services.AddLogging();
+        services.AddDataProtection();
+        services.AddSecurity();
+        // The per-environment override the docker-env2 cluster uses to avoid clobbering the
+        // primary cluster's cookie on localhost.
+        services.Configure<SecurityOptions>(o => o.CookieName = "ZB.MOM.WW.ScadaBridge.Auth.env2");
+
+        using var provider = services.BuildServiceProvider();
+        var cookieOptions = provider
+            .GetRequiredService<IOptionsMonitor<Microsoft.AspNetCore.Authentication.Cookies.CookieAuthenticationOptions>>()
+            .Get(Microsoft.AspNetCore.Authentication.Cookies.CookieAuthenticationDefaults.AuthenticationScheme);
+
+        Assert.Equal("ZB.MOM.WW.ScadaBridge.Auth.env2", cookieOptions.Cookie.Name);
+        // The name override must be purely additive — it must not reset the hardened defaults.
+        Assert.True(cookieOptions.Cookie.HttpOnly);
+        Assert.Equal(Microsoft.AspNetCore.Http.SameSiteMode.Strict, cookieOptions.Cookie.SameSite);
+        Assert.True(cookieOptions.SlidingExpiration);
+    }
+
+    [Theory]
+    [InlineData("")]
+    [InlineData("   ")]
+    public void AddSecurity_AuthCookie_BlankCookieName_FallsBackToDefault(string blank)
+    {
+        var services = new ServiceCollection();
+        services.AddLogging();
+        services.AddDataProtection();
+        services.AddSecurity();
+        services.Configure<SecurityOptions>(o => o.CookieName = blank);
+
+        using var provider = services.BuildServiceProvider();
+        var cookieOptions = provider
+            .GetRequiredService<IOptionsMonitor<Microsoft.AspNetCore.Authentication.Cookies.CookieAuthenticationOptions>>()
+            .Get(Microsoft.AspNetCore.Authentication.Cookies.CookieAuthenticationDefaults.AuthenticationScheme);
+
+        // A blank value must never produce an unnamed cookie.
+        Assert.Equal(SecurityOptions.DefaultCookieName, cookieOptions.Cookie.Name);
+    }
+
     // --- Security-001: transport security (now owned by the shared LdapOptions) ---
 
     [Fact]