There is vaguely newsworthy drama in WordPress land, with the relevant point that organisers of community-organized events have been ordered by the WordPress developer/trademark owner share their login credentials for social networks. From an answer on our sister site which links the facebook terms of service this is breaches these ToS. This also says it is similarly a breach to solicit a password.
First thing, you should not share your Facebook password with anyone else. It's a violation of Facebook’s Statement of Rights and Responsibilities to share or solicit a Facebook password.
not share your password, give access to your Facebook account to others or transfer your account to anyone else (without our permission).
I suspect that neither of these things are rare, in that most social media contracts, as well as just about any time one provides a password online, there is a clause forbidding sharing ones password. Also I suspect there are many times where someone in power over another demands their login details.
However this seems legally dangerous. It seems clear breach of contract by at least the party giving up the credentials and possibly the party making the request, and in the UK it seems the use of the credentials by the requester would constitute unauthorised access to computer material under the Computer Misuse Act 1990 which is a crime. I would imagine in the US one would consider the CFAA, ECPA and the DMCA on finding crimes.
What would be the legal situation if someone requests/demands the login credentials for an online service such as social media against the TOS, the other party gives the credentials and they are used by the requester in a way that would be legal if done by the legitimate owner of the account? Any jurisdiction would be interesting.