Build access token method from the token handler of JWT API.

TokenHandler.cs

private AccessToken BuildAccessToken(User user, RefreshToken refreshToken)
{
    var accessTokenExpiration = DateTime.UtcNow.AddSeconds(_tokenOptions.AccessTokenExpiration);

    var securityToken = new JwtSecurityToken
    (
        issuer : _tokenOptions.Issuer,
        audience : _tokenOptions.Audience,
        claims : GetClaims(user),
        expires : accessTokenExpiration,
        notBefore : DateTime.UtcNow,
        signingCredentials : _signingConfigurations.SigningCredentials
    );

    var handler = new JwtSecurityTokenHandler();
    var accessToken = handler.WriteToken(securityToken);

    return new AccessToken(accessToken, accessTokenExpiration.Ticks, refreshToken);
}