Override Microsoft Identity Auth Error Page to Fix Misleading Production Message

Replace the default misleading “Development Mode” error page generated by Microsoft.Identity.Web.UI with a clean, branded, user-friendly authentication error page in Production, while ensuring Serilog logs and emails identity errors.

Clarifications & Architecture

1. Scope of /MicrosoftIdentity/Account/Error:
   • This page is only navigated to during Microsoft Identity / Azure AD B2C authentication flows (e.g., OIDC callback errors, session timeouts, login cancellation).
2. Impact on Standard Application Errors:
   • All standard application errors (database exceptions, unhandled runtime errors, etc.) remain completely unaffected. They continue to be caught by app.UseExceptionHandler("/Error") (Pages/Error.cshtml) and logged/emailed by Serilog automatically.
3. Serilog Integration for Identity Errors:
   • Because Microsoft Identity UI catches OIDC errors gracefully and redirects to /MicrosoftIdentity/Account/Error, ASP.NET Core doesn’t treat them as unhandled 500 crashes.
   • We will inject ILogger<ErrorModel> into our custom ErrorModel (Error.cshtml.cs) to explicitly log a Serilog Error event when this page renders. This ensures identity failures are written to logs/errors-.txt and sent via Serilog email (team.crystal@outlook.com).

User Review Required

Proposed Changes

Web Project (ErpCrystal_MFG.Web)

[NEW] Error.cshtml

• Local Razor Page shadowing Microsoft.Identity.Web.UI’s embedded error page.
• Render Request ID if available.
• Display a clean generic card in Production (<environment exclude="Development">) with instructions to try logging in again or file a support request.

[NEW] Error.cshtml.cs

• PageModel for Areas/MicrosoftIdentity/Pages/Account/Error.cshtml.
• Inject ILogger<ErrorModel> and ILoginErrorAccessor.
• Log _logger.LogError(...) on OnGet() so Serilog records the identity error and sends an email alert.

Verification Plan

Automated Build Verification

• Run dotnet build ErpCrystal_MFG.Web/ErpCrystal_MFG.Web.csproj to confirm Razor Compilation and C# code build without errors.

Manual Verification

• Verify navigating to /MicrosoftIdentity/Account/Error renders the new layout and logs a Serilog warning/error entry.