[Bug] Logs error about cache serialization even though one is provided?

Logs and network traces 12:58 [Error] [] : False MSAL 4.37.0.0 MSAL.NetCore .NET 5.0.11 Microsoft Windows 10.0.19043 [11-04 11:58:00.33 - 9c02650f-5821-42a0-97c6-a8a7f269e513] The default token cache provided by MSAL is not designed to be performant when used in confidential client applications. Please use token cache serialization. See https://aka.ms/msal-net-cca-token-cache-serialization.

Which version of MSAL.NET are you using? MSAL 4.37.0.0 MSAL.NetCore .NET 5.0.11 Microsoft Windows 10.0.19043

Platform .NET Core 5

What authentication flow has the issue?

• Desktop / Mobile
  • Interactive
  • Integrated Windows Authentication
  • Username Password
  • Device code flow (browserless)
• Web app
  • Authorization code
  • On-Behalf-Of
• Daemon app
  • Service to Service calls

Other? We are using MSAL-angular to sign in to azure ad and the token is sent from the client to a web api endpoint that is protected by that. We are using msal for some endpoints and cookies for the rest.

Is this a new or existing app? c. This is a new app or experiment.

Repro

 var authBuilder = services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme);

            authBuilder.AddMicrosoftIdentityWebApi(Configuration)
                    .EnableTokenAcquisitionToCallDownstreamApi()
                        .AddMicrosoftGraph(Configuration.GetSection("DownstreamAPI"))
                        .AddInMemoryTokenCaches();

            authBuilder.AddCookie("Samla", options =>
            {
                options.Cookie.Name = "auth_cookie";
                options.Cookie.HttpOnly = true;
                options.Cookie.SameSite = SameSiteMode.None;
                options.SlidingExpiration = true;
                options.ExpireTimeSpan = TimeSpan.FromDays(14);
                options.Events = new CookieAuthenticationEvents
                {
                    OnRedirectToLogin = redirectContext =>
                    {
                        redirectContext.HttpContext.Response.StatusCode = 401;
                        return Task.CompletedTask;
                    },

                };
            });

Expected behavior No errors is expected in the log if we add .AddInMemoryTokenCaches()

Actual behavior Getting errors in the log saying that a cache serialization has not been provided

Additional context / logs / screenshots Add any other context about the problem here, such as logs and screenshots.

[bgavrilMS]

https://github.com/AzureAD/microsoft-authentication-library-for-dotnet/blob/master/src/client/Microsoft.Identity.Client/Internal/Requests/RequestBase.cs#L358

Having looked at this in more detail, it looks like we are logging this error in the correct place:

• confidential client flows except client_credentials
• if cache serialization is not enabled.

But the error message is not good:

• “The default token cache provided by MSAL is not designed to be performant when used in confidential client applications. Please use token cache serialization. See https://aka.ms/msal-net-cca-token-cache-serialization.”

It should say:

• “Only in-memory caching is used. The cache is not persisted and will be lost if the machine is restarted. It also does not scale for a web app or web api, where the number of users can grow large. Production apps should use distributed caching. See https://aka.ms/msal-net-cca-token-cache-serialization”.

And as per feedback, this should be a warning, not an error.

[Abrissirba]

I would prefer to be aware of all potentiall errors in development and not being suprised by it when I go to production.

I am using 1.20.0 of Microsoft Identity Web