OAuth (preferred)

OAuth is the preferred authentication mechanism for both web and installed apps. Using the scope https://www.google.com/reader/api/ obtain a request token, authorize it, exchange it for an access token, and make requests as usual, passing in the OAuth token in the Authorization: HTTP header. You may find the OAuth Playground useful in experimenting with all this.

The https://www.google.com/reader/atom/ and https://www.google.com/reader/subscription/export scopes are supported as well for applications wish to use the Atom and OPML outputs. Additionally, HTTP versions of these HTTPS schemes are also available.

ClientLogin

Installed (desktop) apps may also use ClientLogin to perform authenticated requests against Google Reader's API. The app provides the user's username and password, and obtains an authentication token in response (the value after Auth= in the response). That token can be be included as an HTTP header in all requests (format Authorization:GoogleLogin auth=<auth value>).

service should be set to reader. accountType should be set to GOOGLE (Google Reader does not support hosted accounts).

Sample curl request to get the authentication token:

$ curl -d accountType=GOOGLE \
  -d Email=username@gmail.com \
  -d Passwd=password \
  -d service=reader \
  https://www.google.com/accounts/ClientLogin
SID=<SID value> # ignored
LSID=<LSID value> # ignored
Auth=<auth value>

Sample curl request that uses the authentication token:

$ curl -H "Authorization:GoogleLogin auth=<auth value>" http://www.google.com/reader/api/0/user-info
{
  "userId":"123",
  "userName":"Name",
  "userProfileId":"123",
  "userEmail":"username@gmail.com",
  "isBloggerUser":true,
  "signupTimeSec":0,
  "publicUserName":"username"
}

Clients should also handle CAPTCHA challenges, see the documentation for more information.