[UPHPU] Automate third-party site login?

[Chris Wood]

I have an odd situation where I want to link from one site to a third-party
site and automatically log the user in.  The other site is happy to let me
do this if I can figure it out.  I tried talking them into providing access
to the data on their site in other ways, but this is the only way they will
do it due to getting burned in the past.

The reason I want to link it this way is that I don't want to have to tell
users what the username/password is for the site and then have to tell them
again every time I change the password (which will happen as I gain/lose
users).

Is there any way to do this with PHP/javascript, etc?

Chris