While it seems (based on other comments) that the product mentioned here doesn't do that, if the phone has an alternative link (e.g. GPRS / 3G / 4G) data link t

While it seems (based on other comments) that the product mentioned here doesn't do that, if the phone has an alternative link (e.g. GPRS / 3G / 4G) data link to the server that stores the credentials, it would be possible to make this more secure. For example, suppose Alice wants to connect to Bob's 802.11g wifi hotspot using 802.11i-2004 (WPA2) authentication in PSK mode. Charlie and Bob have the password; neither want to give it to Alice, but Charlie wants to facilitate Alice to access Bob's system. The first step of the normal WPA2-PSK process is to take the password and generate the Pairwise Master Key (PMK) by putting the password through a key derivation function (PBKDF2-SHA1). However, the PMK is essentially just a stretched version of the password - so we will assume Charlie also doesn't want to share that. To continue with the connection, Alice needs to compute the same Pairwise Transient Key (PTK) as Bob. The PTK is a hash function computed from the PMK, Alice's random nonce, Bob's random nonce, Alice's MAC address, and Bob's MAC address. Alice could send the latter four pieces of information to Charlie over the existing link, then Charlie could send the computed PTK back to Alice, allowing Alice to make the 802.11g connection without revealing the PMK or password to Alice. A similar way of transferring enough information to allow the connection to continue is likely possible for other authentication modes like the various 802.11X options. Of course, implementing this would probably require, at least, a rooted phone (for example, to replace the stock wpa_supplicant on Android). Also, the server would need to store the password or PMK itself (either in plaintext or encrypted with a key that is kept available at all times to process incoming requests), so it would have a huge database of credentials that could be compromised.