A Claims Provider in SharePoint 2010 issue claims and pakages claims into securty tokens. how claim wok. first user get the token from claim provider in sp then login into SharePoint 2010. mostly it use for to augment claims and provide name resolution.
Claims augmentation start after user login to Claims Authentication Site. to remeber that the user is running on claim in authentication sharepoint 2010 site.it can be
1 widdows (NTLM(Out of box default.) or Kerberos Protocol)
2 form-Based Auth (by using ASpnet membership role provider framework)
3 Security Assertions Markup Language (SAML) claims (when you log on by using a security token service (STS), such as Active Directory Federation Services (AD FS) 2.0)
like most commonly problem in share point 2010 with search resolve in People Picker for trusted Login Providers. for example if your typing in Seach of public picker to validate user and its not resolving. to solve this Problem in sp2010 you have two ways.
Custom Claim Provider
Replace the Dfault Claims Provider with your own.
$trusted = Get-SPTrustedIdentityTokenIssuer -Identity "Trusted Login Provider Name Goes Here"
$trusted.ClaimProviderName = “name of your custom claim provider” //in your claim provider you need to override the SPClaimProvider.Name; use that value here
Writte Code for claim Provider Walkthrough
Creating Custom Claim Provider
Claim Based Architecture