• Add AspNet.Identity.MySQL from NuGet or GitHub to your project.
• Add MySql.Data from NuGet to your project
• Add a MySQL schema and create the tables
• Apply changes (or here and here) to your project
• Change connection string to
  

<add name="DefaultConnection" connectionString="Server=localhost;Port=3306;Database=<schema_name>;Uid=<username>;Pwd=<password>;" providerName="MySql.Data.MySqlClient" />

• in case of a null reference exception, use

var manager = new ApplicationUserManager(new UserStore<ApplicationUser>(new MySQLDatabase("AuthConnection")));