fix(security): make auth-cookie SecurePolicy configurable for HTTP-only deployments

The cookie SecurePolicy was hard-coded to Always, so the auth cookie was always
marked Secure and the browser never sent it over plain HTTP — making login
impossible on the HTTP-only Docker dev cluster (login succeeded server-side but
every following request was unauthenticated). Add SecurityOptions.RequireHttps-
Cookie (default true — production stays HTTPS-only); when false the cookie uses
SameAsRequest. The docker/ central nodes set it false.

src/ScadaLink.Security/SecurityOptions.cs

@@ -92,4 +92,14 @@ public class SecurityOptions
     /// Minutes before token expiry to trigger refresh.
     /// </summary>
     public int JwtRefreshThresholdMinutes { get; set; } = 5;
+
+    /// <summary>
+    /// When true (default) the authentication cookie is always marked
+    /// <c>Secure</c> (sent only over HTTPS) — the correct production setting,
+    /// since the cookie carries the embedded JWT bearer credential. Set false
+    /// for an HTTP-only deployment such as the local Docker dev cluster: the
+    /// cookie then uses <c>SameAsRequest</c>, so it is still <c>Secure</c> on
+    /// any HTTPS request but is usable over plain HTTP.
+    /// </summary>
+    public bool RequireHttpsCookie { get; set; } = true;
 }

src/ScadaLink.Security/ServiceCollectionExtensions.cs

@@ -21,9 +21,8 @@ public static class ServiceCollectionExtensions
                 options.Cookie.Name = "ScadaLink.Auth";
                 options.Cookie.HttpOnly = true;
                 options.Cookie.SameSite = Microsoft.AspNetCore.Http.SameSiteMode.Strict;
-                // The cookie carries the embedded JWT (a bearer credential); never
-                // transmit it over plain HTTP. Design: "HttpOnly and Secure (requires HTTPS)".
-                options.Cookie.SecurePolicy = Microsoft.AspNetCore.Http.CookieSecurePolicy.Always;
+                // Cookie.SecurePolicy is set in the PostConfigure block below so it
+                // can honour SecurityOptions.RequireHttpsCookie.
             });
 
         // CentralUI-005: configure the cookie session as a sliding window so the
@@ -46,6 +45,14 @@ public static class ServiceCollectionExtensions
                 var idleMinutes = securityOptions.Value.IdleTimeoutMinutes;
                 cookieOptions.ExpireTimeSpan = TimeSpan.FromMinutes(idleMinutes);
                 cookieOptions.SlidingExpiration = true;
+
+                // The cookie carries the embedded JWT bearer credential. Production
+                // keeps it HTTPS-only (Always); an HTTP-only deployment (e.g. the
+                // local Docker dev cluster) opts out via RequireHttpsCookie=false and
+                // uses SameAsRequest — still Secure on any HTTPS request.
+                cookieOptions.Cookie.SecurePolicy = securityOptions.Value.RequireHttpsCookie
+                    ? Microsoft.AspNetCore.Http.CookieSecurePolicy.Always
+                    : Microsoft.AspNetCore.Http.CookieSecurePolicy.SameAsRequest;
             });
 
         services.AddScadaLinkAuthorization();