Doing a bit of checking, it appears that the direct link to the webcast is here.
If you check in a little early, they have a five-minute video of highlights from previous awards ce
No password is needed to watch, it will just be an open live stream.
I'm a bit uncertain about the exact online address for all this, since I've been given different information. But I suspect the safest best is to click here -- it's being hosted through the Los Angeles Times website -- and if the show is streaming on this page, they'll have a link there where clicking through will take you to the show.
(If you might be interested in watch, best to simply click that link above now and bookmark it for tomorrow.)
Just in case, here is another L.A. Times page that may have the broadcast or will get you there. The confusion is that the link above is the one the WGA sent out. But it goes to a news story on the Los Angeles Times about the awards show. The article, however, has a separate link here that takes you to their Envelope page, where they say the webcast will be. At the moment, though, there are just a lot of entertainment news stories and videos, and no streaming, so it's hard to be sure what gives.
I suspect the webcast will be on this "second" link, and is the direct one. But either link should get you to the show.
Again, the WGA Awards starts at 6 PM (Los Angeles time) with pre-game festivities starting at 5 PM.