Build me a wordpress page which will launch a URL from a user's profile.

I would like some code written for my Wordpress site: 1) Add a new custom field in the Wordpress user profile called "Sharepoint". This will contain a fully-qualified URL. This needs to support up to 200 characters, the links I will be storing are dynamic links, and will be too long for the already-existent 'Website' profile field. 2) Create a page or link or some other object that will be activated via clicking a link in the primary header navigation bar (see screenshot, the nav item circled in red is how I would like this launch to be triggered). When I click on that link, if the user is logged in, the page should trigger some PHP or Javascript or something, which will retrieve the new custom "Sharepoint" field from the logged-in user's profile, and launch the URL in a new tab. This will not be an internal link, it will go to an external page, which will be a shared link to my Sharepoint site. 3) If the user is not logged in, the screen should be redirected to the normal WP login screen. After login, the process in #1 should happen -- go get the "Sharepoint" field and open a new tab to that link. 4) If the new custom "Sharepoint" field is not populated, an error page should pop up, saying "You do not have a valid Sharepoint URL. Please contact support".