It's not a scam. Some websites require a special client certficate for access. If you don't have that certficate, you'll have to contact the site operator to find out how to get one.
Sometimes the problem is caused by a web server that is configured to request an optional client certificate. Safari treats the request as mandatory. In that case, other browsers such as Firefox and Chrome may be able to connect to the site, because they ignore the request.
The first time you were prompted for a certificate, you may have clicked through a dialog that requested access to the Apple certificate in your keychain that is used to secure the iMessage service. In that case, you may be able to regain access to the site in Safari by doing as follows.
Back up all data.
Launch the Keychain Access application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad and start typing the name.
Search the list of keychain items for one with the Name of the site in question and the Kind "identity preference."
Delete the item by selecting it and pressing the delete key. The next time you visit a site that prompts for an optional client certificate, cancel out of the prompt. You may have to do this several times before the server stops asking.
