Please be cautious about giving out your password, as a recipient can gain full access to your account. If you are usure about an application, revoke its access on the Apps tab of your account settings page and change your password. However, some applications may need your username and password to function.
Apps that may safely require your username and password:
Apps to which you should never provide your username and password:
If you're having trouble with a third party app, please see this article for troubleshooting tips.