microsoft-authentication-library-for-dotnet: [Bug] Inconsistent results using OBO flow

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Which version of MSAL.NET are you using? Microsoft.Identity.Client 4.34.0 Microsoft.Identity.Web 1.14.0

Platform .Net Framework 4.7.2

What authentication flow has the issue?

• 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?

• Sign in with mobile app
• Call private API which creates confidential client application and calls AquireTokenOnBehalfOf
• Call downstream graph API (outlook)

Is this a new or existing app? a. The app is in production, and I have upgraded to a new version of MSAL.

Repro

    public class MicrosoftService : IMicrosoftService
    {
        public IConfidentialClientApplication ConfidentialClientApplication { get; set; }
        private readonly ICompanyUserRepo _userRepo;
        private readonly IAuthenticationSettings _authenticationSettings;
        private readonly IDatabaseSettings _databaseSettings;

        public MicrosoftService(
            ICompanyUserRepo userRepo,
            IAuthenticationSettings configuration,
            IDatabaseSettings databaseSettings)
        {
            _userRepo = userRepo;
            _authenticationSettings = configuration;
            _databaseSettings = databaseSettings;

            ConfidentialClientApplication = BuildApp();
        }

        public async Task GetAccessTokenAndUpdateUser(string userId, IEnumerable<string> scopes, string jwt)
        {
            await AquireTokenOnBehalfOf(scopes, jwt);

            var user = _userRepo.GetByIdAndPartitionKeyOrDefault(userId, userId);
            user.MicrosoftIdentity = jwt;

            _userRepo.Update(user);
        }

        public async Task<AuthenticationResult> GetToken(string userId, IEnumerable<string> scopes)
        {
            var user = _userRepo.GetByIdAndPartitionKeyOrDefault(userId, userId);
            var jwt = user.MicrosoftIdentity;

            return await AquireTokenOnBehalfOf(scopes, jwt);
        }

        public async Task RevokeToken(string userId, IEnumerable<string> scopes)
        {
            var user = _userRepo.GetByIdAndPartitionKeyOrDefault(userId, userId);
            var authResult = await AquireTokenOnBehalfOf(scopes, user.MicrosoftIdentity);

            await ConfidentialClientApplication.RemoveAsync(authResult.Account);
            user.MicrosoftIdentity = null;

            _userRepo.Update(user);
        }

        private async Task<AuthenticationResult> AquireTokenOnBehalfOf(IEnumerable<string> scopes, string jwt)
        {
            var userAssertion = new UserAssertion(jwt);
            var res = await ConfidentialClientApplication.AcquireTokenOnBehalfOf(scopes, userAssertion).ExecuteAsync();

            return res;
        }

        private IConfidentialClientApplication BuildApp()
        {
            // The application which retreives the auth token must also use the same client id and redirect url when requesting the token. The auth token from the response is then passed to the AquireTokenByAuthorisationCode method below. 

            IConfidentialClientApplication app = ConfidentialClientApplicationBuilder
                .Create(_authenticationSettings.MicrosoftRevokeAppId)
                .WithRedirectUri(_authenticationSettings.EmailScanWebAppBaseUrl + _authenticationSettings.MicrosoftRedirectAction)
                .WithClientSecret(_authenticationSettings.MicrosoftRevokeAppSecret)
                .WithTenantId(_authenticationSettings.MicrosoftTenantId)
                .Build();

            IMsalTokenCacheProvider cosmosTokenCacheProvider = CreateCosmosTokenCacheSerialiser();
            cosmosTokenCacheProvider.Initialize(app.UserTokenCache);

            return app;
        }

        private IMsalTokenCacheProvider CreateCosmosTokenCacheSerialiser()
        {
            IServiceCollection services = new ServiceCollection().AddLogging();
            var cosmosConnectionString = string.Format("AccountEndpoint={0};AccountKey={1};", _databaseSettings.RevokeGlobalDatabaseUri, _databaseSettings.RevokeGlobalDatabaseKey);

            services.AddDistributedTokenCaches();
            services.AddCosmosCache((CosmosCacheOptions cacheOptions) =>
            {
                cacheOptions.DatabaseName = _databaseSettings.RevokeGlobalDatabase;
                cacheOptions.ContainerName = _authenticationSettings.CosmosMsalContainer;
                cacheOptions.CreateIfNotExists = true;
                cacheOptions.ClientBuilder = new CosmosClientBuilder(cosmosConnectionString);
            });

            IServiceProvider serviceProvider = services.BuildServiceProvider();
            IMsalTokenCacheProvider msalTokenCacheProvider = serviceProvider.GetRequiredService<IMsalTokenCacheProvider>();

            return msalTokenCacheProvider;
        }
    }
}

Expected behavior A token is retrieved which can be used to call the downstream api

Actual behavior Sometimes the token is retrieved, sometimes it returns this error instead:

AADSTS70000: The request was denied because one or more scopes requested are unauthorized or expired. The user must first sign in and grant the client application access to the requested scope.\r\nTrace ID: 19a4f1a4-09cd-4729-8ccb-b1299cc37600\r\nCorrelation ID: 34dc13fe-7c6e-49af-acdc-e85b62088927\r\nTimestamp: 2021-07-15 13:37:24Z

Possible solution

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