You are not giving them your Google credentials - you are allowing them to use Google to sign you in, confirming your identity (name, email). Technical details are here: http://code.google.com/apis/accounts/docs/OpenID.html
- the key point is that your password remains private between you and Google.
Comments
not trusting them with any creds
Aside: what is the risk associated with giving someone your google authentication?
You are not giving them your Google credentials - you are allowing them to use Google to sign you in, confirming your identity (name, email). Technical details are here: http://code.google.com/apis/accounts/docs/OpenID.html - the key point is that your password remains private between you and Google.