LinkedIn REST URL (Step 1 - Obtain Request Token)

Hello,

I have had the pleasure to deal with the LinkedIn REST URLs these past few days.

There are some Ruby, Python, etc wrappers, but there is none for .NET.

There's not a lot of examples in .NET either.

So, I decided to write my own wrapper with the help of OAuthBase.cs.

Now, the basic authentication was already documented on https://developer.linkedin.com/documents/authentication.
There are 3 steps to be authenticated by LinkedIn:

1. Obtain a request token
2. Let users authorize our access to their info (http://dailyprogrammingtalk.blogspot.com/2012/11/linkedin-rest-api-step-2-obtain.html)
3. Obtain an access token

I will focus on getting a request token on this blog post.

One thing that's not clear is having 'scope' in the querystring parameters.
I kept getting the signature_invalid 401 error.

It says on the documentation that we only need to make a POST request to https://api.linkedin.com/uas/oauth/requestToken?scope=r_basicprofile+r_emailaddress, which is misleading. I have to use a space instead of the plus sign.

So, I made a POST request to 

https://api.linkedin.com/uas/oauth/requestToken?scope=r_basicprofile r_emailaddress

I generated a signature using the url above, but without a token and token secret.

OAuthBase oauth = new OAuthBase();
string linkedinUrl = "https://api.linkedin.com/uas/oauth/requestToken?scope=r_basicprofile r_emailaddress"

string url = String.Empty;

string urlParameters = String.Empty;
string timeStamp = oauth.GenerateTimeStamp();
string nonce = oauth.GenerateNonce();

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(linkedinUrl);
request.Method = "POST";
string signature = oauth.GenerateSignature(new Uri(linkedinUrl), consumerKey, consumerSecret, String.Empty, String.Empty, "POST", timeStamp, nonce, out url, out urlParameters);

Then, I created an 'Authorization' header for the request, which contains:

StringBuilder header = new StringBuilder("OAuth ");
header.AppendFormat("oauth_consumer_key=\"{0}\"", consumerKey);
header.AppendFormat(", oauth_signature_method=\"{0}\"", "HMAC-SHA1");
header.AppendFormat(", oauth_signature=\"{0}\"", MsSecurity.Encoder.UrlEncode(signature));
header.AppendFormat(", oauth_nonce=\"{0}\"", nonce);
header.AppendFormat(", oauth_timestamp=\"{0}\"", timeStamp);
header.AppendFormat(", oauth_version=\"{0}\"", "1.0");

The MsSecurity is an alias for the AntiXss library. I need to url-encode the signature. Otherwise, it won't work.

Now, I no longer get the 401 error. Hope this helps someone obtain their request token on LinkedIn.

Let's move on to Step 2: http://dailyprogrammingtalk.blogspot.com/2012/11/linkedin-rest-url-step-2-obtain.html