Java based user authentication

Can someone point me in the direction of a good Java library to use to handle basic user login/authentication.

I am looking for a competent I can integrate in开发者_如何学Goto a custom app to handle simple user/name password authentication and send account validation/password reset emails.

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Maybe you could use the JAAS (Java Authentication and Authorization Service). Look at the user guide and to get an overview of it look at the tutorials and simple programs of this guide.

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Filters would work: http://java.sun.com/products/servlet/Filters.html