WP login on external .php page?

Client has thrown me a complete noodlescratcher, and after poring over the plugin gallery and forums I haven’t found a solution yet… help? Anybody?

I have an instance of WP installed on a server at client.com/business/agents — it’s a locked-down version of WP that allows registered access to information that they don’t want shared otherwise on their main website. Easy enough.

But now they want to add a login box to the sidebar of the existing page at client.com/business, which obviously sits outside of the WP install. The site is built in PHP, but other than a coded text link there’s no existing database connection between client.com/business and client.com/business/agents.

Question is, how can I add a login form to a page outside of WP, but on the same server, that can authenticate users and redirect them to the main WP page?

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nevermind, I’m a moron.
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Using the loginform code with the action pointing to the wp-login.php page works.