Few have noticed that Amazon still uses (at the time of this writing) OpenID for user authentication. Check it out yourself: go to www.amazon.com, and click the Sign In button. Then observe the browser address bar. You see something similar to the following, which is an OpenID authentication request:
https://www.amazon.com/ap/signin?_encoding=UTF8&
openid.assoc_handle=usflex&
openid.claimed_id= http://specs.openid.net/auth/2.0/identifier_select&
openid.identity= http://specs.openid.net/auth/2.0/identifier_select&
openid.mode=checkid_setup&
openid.ns=http://specs.openid.net/auth/2.0&
openid.ns.pape= http://specs.openid.net/extensions/pape/1.0&
openid.pape.max_auth_age=0&
openid.return_to= https://www.amazon.com/gp/yourstore/home
https://www.amazon.com/ap/signin?_encoding=UTF8&
openid.assoc_handle=usflex&
openid.claimed_id= http://specs.openid.net/auth/2.0/identifier_select&
openid.identity= http://specs.openid.net/auth/2.0/identifier_select&
openid.mode=checkid_setup&
openid.ns=http://specs.openid.net/auth/2.0&
openid.ns.pape= http://specs.openid.net/extensions/pape/1.0&
openid.pape.max_auth_age=0&
openid.return_to= https://www.amazon.com/gp/yourstore/home