return multiple values in public string method

Question

public string post(login lg) {
try{
query here
return (particular user data here)
}
catch(){
throw;
}
}

I am using web API controller

 

my code:

public string Post(login lg)
{
List<login> log = new List<login>();
try {
string query = @"select email,upassword,status,userid from signup where email='" + lg.email + "' and upassword='" + lg.upassword + "' and status=1";
DataTable dt = null;
using(SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["rhymeDB"].ConnectionString))
using(SqlCommand cmd = new SqlCommand(query, con))
using (SqlDataAdapter da = new SqlDataAdapter(cmd))
{
DataSet ds = new DataSet();
da.Fill(ds);
if (ds.Tables.Count > 0)
{
dt = ds.Tables[0];
}
if (dt.Rows.Count > 0)
{
login lgg = new login();
lgg.email = dt.Rows[0]["email"].ToString();
lgg.userid = dt.Rows[0]["userid"].ToString();
log.Add(lgg);
return ???
}
else
{
return "invalid";
}
}
}
catch(Exception ex)
{
return ex.ToString();
}
}