The OAuth2's Redirect Url on Sharepoint get HttpStatus 403. The SharePoint's Authentication type is Claims Based Authentication

I wrote a yammer webpart for sharepoint2010, in the webpart I use OAuth2 to get the access token from the yammer.The redirect url is a aspx page written in the webpart, when the yammer server redirects to the rdirect url, the request get 403 error.The sharepoint's authentication type is "Claims Based Authentication".If the sharepoint's authentication type is "Classic Mode Authentication", the yammer server can access the redirect url. 

Can anyone help me?