CustomExternalUserBuilder not getting called sitecore 9.3

Question

We have added identity provider for Azure B2C for login into sitecore websites. We need to change the username of virtual user that is created by sitecore after authentication. For that, below code is added and an entry is made to the config file but the code is not getting called. Please let me know what else we need to add?

Thank you in advance.

 public class CustomExternalUserBuilder : ExternalUserBuilder
    {
        private readonly IHashEncryption _hashEncryption;

        public CustomExternalUserBuilder(
          ApplicationUserFactory applicationUserFactory,
          IHashEncryption hashEncryption)
        {
            Assert.ArgumentNotNull((object)applicationUserFactory, nameof(applicationUserFactory));
            Assert.ArgumentNotNull((object)hashEncryption, nameof(hashEncryption));
            this._hashEncryption = hashEncryption;
            this.ApplicationUserFactory = applicationUserFactory;
        }

        public bool IsPersistentUser { get; set; }

        protected ApplicationUserFactory ApplicationUserFactory { get; }

        public override ApplicationUser BuildUser(
          UserManager<ApplicationUser> userManager,
          ExternalLoginInfo externalLoginInfo)
        {
            ApplicationUser user = this.ApplicationUserFactory.CreateUser(this.CreateUniqueUserName(userManager, externalLoginInfo));
            user.IsVirtual = !this.IsPersistentUser;
            user.Email = externalLoginInfo.Email;
            return user;
        }

        protected virtual string CreateUniqueUserName(
          UserManager<ApplicationUser> userManager,
          ExternalLoginInfo externalLoginInfo)
        {
            Assert.ArgumentNotNull((object)userManager, nameof(userManager));
            Assert.ArgumentNotNull((object)externalLoginInfo, nameof(externalLoginInfo));
            var identityProvider = this.FederatedAuthenticationConfiguration.GetIdentityProvider(externalLoginInfo.ExternalIdentity)
                                   ?? throw new InvalidOperationException("Unable to retrieve an identity provider for the given identity");
            string domain = (identityProvider).Domain;
            string accountName = externalLoginInfo.ExternalIdentity?.FindFirst("AccountName")?.Value;
            string userName = $"{domain}\\{accountName}";
            return userName;
        }
    }

Config -

<configuration>
  <sitecore>
    <federatedAuthentication>
      <identityProvidersPerSites>
        <mapEntry name="portal" type="Sitecore.Owin.Authentication.Collections.IdentityProvidersPerSitesMapEntry, Sitecore.Owin.Authentication" resolve="true">
          <sites hint="list">
            <site>portal</site>
          </sites>
          <identityProviders hint="list:AddIdentityProvider">
            <identityProvider ref="federatedAuthentication/identityProviders/identityProvider[@id='AzureAdB2C']"/>
          </identityProviders>
          <externalUserBuilder type="Portal.SC.Feature.Login.Pipelines.Owin.CustomExternalUserBuilder, Portal.SC.Feature.Login" resolve="true">
            <param desc="isPersistentUser">false</param>
          </externalUserBuilder>
        </mapEntry>
      </identityProvidersPerSites>
    </federatedAuthentication>
  </sitecore>
</configuration>

Answer 1

The suggestions mentioned in the comment didn't work for us. So, instead of defining username in UserBuilder, we added a method with below code that is getting called from our Login Action -

 string userName = $"{Context.Domain.Name}\\{userId}";
                    Sitecore.Security.Accounts.User virtualUser = AuthenticationManager.BuildVirtualUser(userName, true);
                    virtualUser.SetRoles(user, account, _currentPortalId);
                    AuthenticationManager.Login(virtualUser);

This code runs without any errors and we are able to get required username in Context.User.