Desired workflow:

1. I navigate to the APL login page https://austin.bibliocommons.com/user/login
2. I invoke a bookmarklet on the login page that opens a new browser window/tab
3. In the second tab, I navigate here—to a locally saved copy of (a facsimile of) my library card
4. I invoke a bookmarklet on my library card to send the relevant details to the APL login page using window.postMessage
5. The bookmarklet set up in step 2 receives the details, fills in the login form, and automatically "garbage collects" the second tab

Some other thoughts: We can maintain a personal watchlist/readlist similarly. This document (patron ID "page") itself is probably not a good place for this. It is, however, a good place to reproduce a convenient copy of the necessary bookmarklets. (With this design, only one browser-managed bookmarklet would be necessary; with both bookmarklets being part of the document contents, the second bookmarklet used for step 4 can just be invoked directly from the page itself—no need to follow through on actually bookmarking it.)