How to use identity api on existing project (MVC)

public class ApplicationDbContext : IdentityDbContext
{
    public ApplicationDbContext(DbContextOptions options)
        : base(options)
    {
    }

    public DbSet MyTable1 { get; set; }
    public DbSet MyTable2 { get; set; }

    // Identity API's DbSets are already included in IdentityDbContext
}

Check with the database schema used by the Identity API. Next create a new database context that will share the same database as your existing project. This context will contain the Identity API's tables and your application's tables.

In the Startup.cs file, configure Identity API to use your shared database context.

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext(options =>
        options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

    services.AddIdentity()
        .AddEntityFrameworkStores()
        .AddDefaultTokenProviders();
}