I'm building an application in PHP and MySql that will allow people to sign in with their Salesforce ID, Password and Token and then they will receive a report based on their contacts and opportunities. Are there any extra security measures that I should take to save them in a mysql database? Thanks!
You should do an OAuth login flow and store the refresh_token rather than storing raw credentials. Encrypting the value and managing the key outside of the db would help increase security as well.
Also, presumably you're planning to send them this report on a regular basis? otherwise there's no need to store the credentials or token at all.