Merge branch 'v14/dev' into v15/dev

# Conflicts:
#	src/Umbraco.Infrastructure/Runtime/FileSystemMainDomLock.cs
#	src/Umbraco.Web.Common/Views/UmbracoViewPage.cs

src/Umbraco.Web.Common/Extensions/HttpContextExtensions.cs

@@ -62,9 +62,16 @@ public static class HttpContextExtensions
         // Update the HttpContext's user with the authenticated user's principal to ensure
         // that subsequent requests within the same context will recognize the user
         // as authenticated.
-        if (result.Succeeded)
+        if (result is { Succeeded: true, Principal.Identity: not null })
         {
-            httpContext.User = result.Principal;
+            // We need to get existing identities that are not the backoffice kind and flow them to the new identity
+            // Otherwise we can't log in as both a member and a backoffice user
+            // For instance if you've enabled basic auth.
+            ClaimsPrincipal? authenticatedPrincipal = result.Principal;
+            IEnumerable<ClaimsIdentity> existingIdentities = httpContext.User.Identities.Where(x => x.IsAuthenticated && x.AuthenticationType != authenticatedPrincipal.Identity.AuthenticationType);
+            authenticatedPrincipal.AddIdentities(existingIdentities);
+
+            httpContext.User = authenticatedPrincipal;
         }
 
         return result;

src/Umbraco.Web.Common/Extensions/MemberClaimsPrincipalExtensions.cs

@@ -0,0 +1,18 @@
+using System.Security.Claims;
+using Microsoft.AspNetCore.Identity;
+
+namespace Umbraco.Extensions;
+
+public static class MemberClaimsPrincipalExtensions
+{
+    /// <summary>
+    /// Tries to get specifically the member identity from the ClaimsPrincipal
+    /// </summary>
+    /// <remarks>
+    /// The identity returned is the one with default authentication type.
+    /// </remarks>
+    /// <param name="principal">The principal to find the identity in.</param>
+    /// <returns>The default authenticated authentication type identity.</returns>
+    public static ClaimsIdentity? GetMemberIdentity(this ClaimsPrincipal principal)
+        => principal.Identities.FirstOrDefault(x => x.AuthenticationType == IdentityConstants.ApplicationScheme);
+}