Google GetAccessToken : Bad Request 400

I am using (OpenId+OAuth) hybrid 开发者_如何学编程protocol.

After I redirect user to "https://www.google.com/accounts/o8/ud" with all openid and oauth extension parameters, user is able to see login screen and services I need to access. On successfull login I receive response as following:

http://muUrl.com/...&openid.ns.ext2=http://specs.openid.net/extensions/oauth/1.0&openid.ext2.scope=http://docs.google.com/feeds/&openid.ext2.request_token=4/8GCHDIvtxhbg8gVkfYro7QIFakoB

I understand user is properly logged in and text in bold is authorized token. Then I make call for obtaining access token with all parameters except oauth_verifier as that is not available in hybrid mode. I sign base string using HMAC-SHA1 with key as "consumersecret&" (token secret is yet not available)

I get 400 bad request with signature invalid. Any help or suggestion is highly appreciated to resolve this issue.

pls see Bob and my comments. % escaping can be an issue if you are facing same problem as mine. oauth_verifier is indeed not required in hybrid mode.