ADUserBuilder.cs

using System;
using System.Diagnostics.CodeAnalysis;
using Microsoft.AspNet.Identity;
using Microsoft.AspNet.Identity.Owin;
using Sitecore.Diagnostics;
using Sitecore.Owin.Authentication.Configuration;
using Sitecore.Owin.Authentication.Identity;
using Sitecore.Owin.Authentication.Services;
using Sitecore.SecurityModel.Cryptography;

namespace XXXXX.Foundation.SSO.UserBuilders
{
    public class XXXExternalUserBuilder : DefaultExternalUserBuilder
    {
        public XXXExternalUserBuilder(ApplicationUserFactory applicationUserFactory, IHashEncryption hashEncryption) : base(applicationUserFactory, hashEncryption) { }

        protected override string CreateUniqueUserName(UserManager<ApplicationUser> userManager, ExternalLoginInfo externalLoginInfo)
        { 
            Sitecore.Diagnostics.Log.Debug("CreateUnique UserName",this);

            if (externalLoginInfo != null)
            {
                if (!string.IsNullOrWhiteSpace(externalLoginInfo.Email))
                {
                    return externalLoginInfo.Email;
                }
                else
                {
                    Sitecore.Diagnostics.Log.Debug("empty Email", this);
                    Sitecore.Diagnostics.Log.Debug("default username " + externalLoginInfo.DefaultUserName, this);

                    var validUserName = externalLoginInfo.DefaultUserName.Replace(",", "");
                    return "sitecore\\" + validUserName.Replace(" ", "");

                }
            }
            Sitecore.Diagnostics.Log.Error("null UserInfo when creating UserName", this);

            return "nullUserInfo";
        }
    }
}

AzureAdAuthentication.config

<?xml version="1.0" encoding="utf-8"?>
<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/" xmlns:role="http://www.sitecore.net/xmlconfig/role/" xmlns:localenv="http://www.sitecore.net/xmlconfig/localenv">
  <sitecore localenv:require="uat or prd" role:require="Standalone or ContentDelivery or ContentManagement">
    <federatedAuthentication>
      <identityProvidersPerSites hint="list:AddIdentityProvidersPerSites">
        <!--  Defines a list of providers assigned to all sites.  -->
        <mapEntry name="all sites" type="Sitecore.Owin.Authentication.Collections.IdentityProvidersPerSitesMapEntry, Sitecore.Owin.Authentication" resolve="true">
          <!--
           The list of site names for which the specified identity providers will work.
                         Note: the fedauth.siteNameExpander pipeline processes each site name, which gives the ability to use expressions like
                         "regexp:modules_.*" or "database:web" or "domain:extranet" 
          -->
          <sites hint="list">
            <site>regexp:.*</site>
          </sites>
          <externalUserBuilder type="XXXX.Foundation.SSO.UserBuilders.XXXXExternalUserBuilder, XXXX.Foundation.SSO" resolve="true">
            <IsPersistentUser>true</IsPersistentUser>
          </externalUserBuilder>
        </mapEntry>
      </identityProvidersPerSites>
      <propertyInitializer>
        <maps>
          <map name="set IsAdministrator" type="Sitecore.Owin.Authentication.Services.DefaultClaimToPropertyMapper, Sitecore.Owin.Authentication" resolve="true">
            <data hint="raw:AddData">
              <source name="http://www.sitecore.net/identity/claims/isAdmin" value="true" />
              <target name="IsAdministrator" value="true" />
            </data>
          </map>
          <map name="set Email" type="Sitecore.Owin.Authentication.Services.DefaultClaimToPropertyMapper, Sitecore.Owin.Authentication" resolve="true">
            <data hint="raw:AddData">
              <source name="email"/>
              <target name="Email"/>
            </data>
          </map>
          <map name="set FullName" type="Sitecore.Owin.Authentication.Services.DefaultClaimToPropertyMapper, Sitecore.Owin.Authentication" resolve="true">
            <data hint="raw:AddData">
              <source name="name"/>
              <target name="FullName"/>
            </data>
          </map>
        </maps>
      </propertyInitializer>
    </federatedAuthentication>
  </sitecore>
</configuration>