Please I would like someone to tell me if dotNetOpenAuth single-sign-on.
All I want to achieve is to be able to seamlessly logging to all domains without redirect to third party system for authorisation or Authentication within a mixture programming platforms e.g (PHP or .Net)
DotNetOpenAuth can be used for SSO solutions, but each new web site a user visits does need to perform a redirect to the identity provider. In a controlled SSO environment, that provider may never appear to the user, so the login is totally transparent. There are a couple of samples of an SSO configuration that comes with the DotNetOpenAuth download.
DotNetOpenAuth will help you do what you want to do provided you can support OpenID from PHP. You need to implement a provider (the site that authenticates you against a DB or other store), and a consumer (the site you want to log into).
My recommendation would be to consider the authentication protocol you wish to use rather than a specific library at first. In the case if DotNet OpenAuth it has support for:
These are just a few of the protocols available. You should also look into the SAML family of protocols, in particular SAML 2.0.
There are implementations of SAML for PHP, .NET, and many other platforms. You might want to look at a comparison between OpenID and SAML in order to choose which is better for you.