Dive into OpenID
There are a lot of great guides to getting started with OpenID, including the following:
- http://www.plaxo.com/api/openid_recipe
- http://www.intertwingly.net/blog/2007/01/03/OpenID-for-non-SuperUsers
Get the code
The OpenID community has developed a great wealth of Open Source libraries which implement various OpenID specifications. The libraries listed on the wiki are generally marked if they are beta though use at your own risk.
Read the specifications
OpenID specifications are developed by the community on technical specification mailing lists overseen by specs@openid.net. The current community of editors look to make sure that any draft proposal agrees with the general principals of how OpenID has evolved in terms of being no more complicated than needed to get the job done, modular, free and unencumbered, as well as being further extensible. Only the specifications listed in the “Finalized Specifications” section are considered official OpenID specifications while everything listed in the “Proposed Drafts” section are still being discussed and evolved by the community.