Another issue that you may encounter—and one that may cause you some frustration if you can’t immediately determine what the problem is—has to do with the inability to complete the discovery process for a given OpenID identifier URL.
For instance, consider the following URLs:
When entered into a browser, they would all load the same source site and would not present any challenge in determining what site we are looking for. However, when it comes to OpenID implementations, especially those of older specifications, these differences may create issues during the discovery process.
The problem of the undiscoverable OpenID identifier generally comes up with custom provider implementations of OpenID, where normalization is not being properly applied to a given identifier.
From the consumer point of view, there are two ways to resolve the issue:
If you have control over the identifier URL that is being sent to the provider (that is, if the user doesn’t enter it herself), then you can simply change the URL to exactly what the provider requires.
You can also normalize the URL yourself prior to performing discovery.