I have web application where I store users' password and username. If you logon to this site, you can login with the password and username to have access to your profile.

There is another option that requires you to login to my site from your site and have your profile within your site. This is because you might already have a site that your clients know you with.

This latter part is what I don't know to implement.

I have these ideas:

• Have a fixed IFrame within your site to contain my site: but I am concerned about size/layout since different clients have different layout/size for their content section. I am thinking of how to maintain session too

• A webservice: I don't know how feasible this is since the Password and ID are on my server. You may have to send them back and forth. It means client would have to code with my API. But I am not just returning data, I have to show them a page that contains the profile details

• OpenID, Single-SignOn: Just guessing - but the authentication and data resides on my server. there is nothing to access on your side in this case

• Any other methods/better approach

Examples: like login into facebook within my site and still be able to do post updates, receive notifications

Facebook implement some of these with IFrame e.g. the Like button