All the flickr.auth methods need to be signed.  For example, the description at

http://www.flickr.com/services/api/flickr.auth.getToken.html

says:

Returns the auth token for the given frob, if one has been attached. This method call must be signed.

However, if you use the flickr.reflection.getMethodInfo method (http://www.flickr.com/services/api/flickr.reflection.getMethodInfo.htm) to ask about flickr.auth.getToken via:

http://api.flickr.com/services/rest/?method=flickr.reflection.getMethodInfo&api_key=f2d66368b0bb04060a9f23c3611a733f&method_name=flickr.auth.getToken

(substituting your API Key),

you'll get the following response:

[....]
<method name="flickr.auth.getToken" needslogin="0" needssigning="0" requiredperms="0">
[....]

needssigning should be '1' I think.

I think the same error is in all the flickr.auth methods

Thanks,
-Raymond