Facebook redirect url issue OAuthException

Question

My app was working well for long time, but now I am getting the error from Facebook saying:

Content: {\"error\":{\"message\":\"Error validating verification c

Answer 1

Niranjan, we saw the same error message, precisely. Like you, it started happening this month, without any changes to our code.

We verified carefully that the redirect_uri was indeed exactly the same in both calls - first the authorize call, and second the access_token call.

We filed with Facebook, but they triaged it as "Low": https://developers.facebook.com/bugs/307245456075215?browse=search_51964e3320a5b5556208759

In our case, we were doing something unusual (so this might not be relevant to your case). Our redirect_uri was a URL with another URL embedded as an encoded path element. The URL-within-a-URL, doubly-encoded when passed to FB, had started causing problems with the Facebook API servers.

We resolved this by changing the encoding of the nested URL to a long hex number rather than % encoding, so all Facebook servers see is a simple redirect_uri containing some hex within the path, unaffected by normal URL encoding/decoding.

My suspicion is that Facebook changed the way they encoded/decoded their URL parameters, perhaps decoding twice.

If you're doing something like us, try this approach. If not, try an altogether different and simpler redirect_uri, to see if you can get something to work. And make sure you're correctly encoding/decoding all URL query parameters.