GenerateAuthenticationResultForUserAsync.cs

private async Task<AuthenticationResult> GenerateAuthenticationResultForUserAsync(IdentityUser user)
{
    var tokenHandler = new JwtSecurityTokenHandler();
    var key = Encoding.ASCII.GetBytes(_jwtSettings.Secret);

    var claims = new List<Claim>
    {
        new Claim(JwtRegisteredClaimNames.Sub, user.Email),
        new Claim(JwtRegisteredClaimNames.Jti, Guid.NewGuid().ToString()),
        new Claim(JwtRegisteredClaimNames.Email, user.Email),
        new Claim("id", user.Id)
    };

    var userClaims = await _userManager.GetClaimsAsync(user);
    claims.AddRange(userClaims);

    var tokenDescriptor = new SecurityTokenDescriptor
    {
        Subject = new ClaimsIdentity(claims),
        Expires = DateTime.UtcNow.Add(_jwtSettings.TokenLifetime),
        SigningCredentials =
            new SigningCredentials(new SymmetricSecurityKey(key), SecurityAlgorithms.HmacSha256Signature)
    };

    var token = tokenHandler.CreateToken(tokenDescriptor);

    return new AuthenticationResult
    {
        Success = true,
        Token = tokenHandler.WriteToken(token)
    };
}