A lot depends on what kind of “voting contest” it is. How many candidates are there? How many voters are there? Are the ballots secret? What level of security is required? How strong is the protection against double voting, or can people vote multiple times? Do voters vote for only one candidate, or do they rank several, and if there is ranking, how are the votes counted and the winner selected? Are there real issues, or is this a popularity buy 10best contest votes?
I will only suggest generic advice that applies to essentially all online elections.