One of the things that frustrates customers when implementing claims authentication in SharePoint is how the people picker works for SAML claims users. If you try to add a SAML claims user to a group in SharePoint, anything you type is considered valid. You can fix this issue with custom claim provider.
You can use the below link to create claim provide:
The claims trust is not mentioned in that. So if you create your claim provider, Sharepoint won't recognize your user. You can use below MSDN link for resolution:
https://msdn.microsoft.com/en-us/library/office/gg615945(v=office.14).aspx