ruby-openid SSRF via claimed_id request

Ruby OpenID (aka ruby-openid) through 2.8.0 is vulnerable to SSRF. Ruby-openid performs discovery first, and then verification. This allows an attacker to change the URL used for discovery and trick the server into connecting to the URL, which might be a private server not publicly accessible. Severity can range from medium to critical, depending on how a web application developer chose to employ the ruby-openid library. Developers who based their OpenID integration heavily on the "example app" provided by the project are at highest risk.