DbContextFactory.cs

public class DbContextFactory : IDbContextFactory
{
    private string connectionStringTemplate;

    public string TenantName { get; set; }

    public DbContextFactory(string connectionStringTemplate)
    {
        this.connectionStringTemplate = connectionStringTemplate;
    }

    public CRMContext Create()
    {
        CRMContext context = null;

        if (!string.IsNullOrWhiteSpace(this.TenantName))
        {
            var dbContextOptionsBuilder = new DbContextOptionsBuilder();
            dbContextOptionsBuilder.UseSqlServer(this.connectionStringTemplate
                                   .Replace("{tenant}", this.TenantName));

            context = new CRMContext(dbContextOptionsBuilder.Options);
        }

        return context;
    }
}