Confirm w/ password

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I'm developing an application where a user will need to submit a timesheet, and a digital signature (of sorts) is required.

The idea behind it being, a user hits a submit button, and a modal window appears saying "type your password to submit this timesheet." The users will all have accounts, so they all have passwords...

In the controller, I need an IF statement to check if the password the user typed is the same as the user's password in the database, and if it is, perform action x.

Is there a method to either automatically check this, or a method like getUserPassword(); ? If not, does any one know of a way to do this verification?

Thanks in advance!

focus43