(C# UWP/WinRT) Box.com OAuth2 with JSON Web Tokens

Demonstrates how to obtain an OAuth2 access token using a JSON Web Token. The following explanation is copied from Box Authentication Models

OAuth2 with JSON Web Tokens enables an application to connect directly to Box and obtain authorization to access files and folders without requiring users to log in. Using OAuth2 with JSON Web Tokens an application can provide Box features without users even being aware that Box exists.

Instead of requiring the user to log in to Box, the application generates JSON Web Token (JWT) verified by an RSA keypair. If this authentication succeeds then the application obtains an access token that grants authorization to operate on Box files and folders. This machine-to-machine authentication replaces the first leg of the three-legged authentication process defined by OAuth2, and enables users of your application to work with Box content without seeing Box login requests.

OAuth2 with JSON Web Tokens is designed to be used with Box Platform. You can use OAuth2 with JWT with both Service Accounts and App Users.

Chilkat Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

//  This requires the Chilkat API to have been previously unlocked.
//  See Global Unlock Sample for sample code.

//  When you created an RSA key pair using the Box web user interface,
//  you downloaded a json file named something like "7152782_kkdxptq2_config.json"
//  This contains the following:

//  {
//    "boxAppSettings": {
//      "clientID": "0kraci84o0jfr7yuw596tf394iigzbe7",
//      "clientSecret": "xxxxxxxxxxxxxxxxxxxxxxxxx",
//      "appAuth": {
//        "publicKeyID": "kkdxptq2",
//        "privateKey": "-----BEGIN ENCRYPTED PRIVATE KEY-----\nMIIFDj ... nceU=\n-----END ENCRYPTED PRIVATE KEY-----\n",
//        "passphrase": "xxxxxxxxxxxxxxxxxxxxxxxx"
//      }
//    },
//    "enterpriseID": "7152782"
//  }
// 

//  Load it into a Chilkat JSON object to allow access to the content.
Chilkat.JsonObject jsonRsaKey = new Chilkat.JsonObject();
bool success = jsonRsaKey.LoadFile("qa_data/tokens/7152782_kkdxptq2_config.json");

//  Load the private key into a Chilkat private key object.
string passphrase = jsonRsaKey.StringOf("boxAppSettings.appAuth.passphrase");
string privateKeyPem = jsonRsaKey.StringOf("boxAppSettings.appAuth.privateKey");

Chilkat.PrivateKey rsaKey = new Chilkat.PrivateKey();
success = rsaKey.LoadEncryptedPem(privateKeyPem,passphrase);
if (success != true) {
    Debug.WriteLine(rsaKey.LastErrorText);
    return;
}

//  The JSON Web Token will be created using the JWT class
Chilkat.Jwt jwt = new Chilkat.Jwt();

//  Construct the JOSE header...
Chilkat.JsonObject jose = new Chilkat.JsonObject();
//  Chilkat supports the following algorithms: "RS256", "RS384", and "RS512".  (Chilkat also supports other algorithms that Box does not yet support.)
jose.UpdateString("alg","RS256");
jose.UpdateString("typ","JWT");
jose.UpdateString("kid",jsonRsaKey.StringOf("boxAppSettings.appAuth.publicKeyID"));

//  Now let's build the JWT claims. Most of this is just boilerplate (i.e. the same every time..)
//  The JWT claims contain these required and optional elements:

//  iss (required, String)  The Client ID of the service that created the JWT assertion.
//  sub (required, String)  enterprise_id for a token specific to an enterprise when creating and managing app users, or the app user_id for a token specific to an individual app user.
//  box_sub_type (required, String)  "enterprise" or "user" depending on the type of token being requested in the sub claim.
//  aud (required, String) Always "https://api.box.com/oauth2/token" for OAuth2 token requests
//  jti (required, String) A universally unique identifier specified by the client for this JWT. This is a unique string that is at least 16 characters and at most 128 characters.
//  exp (required, NumericDate) The unix time as to when this JWT will expire. This can be set to a maximum value of 60 seconds beyond the issue time. Note: It is recommended to set this value to less than the maximum allowed 60 seconds.
//  iat (optional, NumericDate) Issued at time. The token cannot be used before this time.
//  nbf (optional, NumericDate) Not before. Specifies when the token will start being valid.
// 

Chilkat.JsonObject claims = new Chilkat.JsonObject();
claims.UpdateString("iss",jsonRsaKey.StringOf("boxAppSettings.clientID"));
claims.UpdateString("sub",jsonRsaKey.StringOf("enterpriseID"));
claims.UpdateString("box_sub_type","enterprise");
claims.UpdateString("aud","https://api.box.com/oauth2/token");

//  Generate 32 random bytes (base64 encoded) for the "jti"
Chilkat.Prng prng = new Chilkat.Prng();
claims.UpdateString("jti",prng.GenRandom(32,"base64"));

//  Set the expiration time to 60 seconds after the current time.
claims.UpdateInt("exp",jwt.GenNumericDate(60));

//  We're going to do the following POST to get a JSON response that contains our OAuth2 access token:

//  	POST /oauth2/token
//  	Content-Type: application/x-www-form-urlencoded
//  	grant_type=urn:ietf:params:oauth:grant-type:jwt-bearer&
//  	assertion=<JWT>&
//  	client_id=<client_id>&
//  	client_secret=<client_secret>

//  First, make the initial connection.
//  A single REST object, once connected, can be used for many Box REST API calls.
//  The auto-reconnect indicates that if the already-established HTTPS connection is closed,
//  then it will be automatically re-established as needed.
Chilkat.Rest rest = new Chilkat.Rest();
bool bAutoReconnect = true;
success = await rest.ConnectAsync("api.box.com",443,true,bAutoReconnect);
if (success != true) {
    Debug.WriteLine(rest.LastErrorText);
    return;
}

//  Add the query params.
//  Calling ClearAllParts is wise if previous requests were sent prior to this one on the same REST object..
rest.ClearAllParts();
rest.AddQueryParam("grant_type","urn:ietf:params:oauth:grant-type:jwt-bearer");
rest.AddQueryParam("client_id",jsonRsaKey.StringOf("boxAppSettings.clientID"));
rest.AddQueryParam("client_secret",jsonRsaKey.StringOf("boxAppSettings.clientSecret"));
rest.AddQueryParam("assertion",jwt.CreateJwtPk(jose.Emit(),claims.Emit(),rsaKey));

string jsonResponse = await rest.FullRequestFormUrlEncodedAsync("POST","/oauth2/token");
if (rest.LastMethodSuccess != true) {
    Debug.WriteLine(rest.LastErrorText);
    return;
}

//  If successful, we'll get a response status code equal to 200,
//  and a JSON response that looks like this:

//  	{
//  	   "access_token": "mNr1FrCvOeWiGnwLL0OcTL0Lux5jbyBa",
//  	   "expires_in": 4169,
//  	   "restricted_to": [],
//  	   "token_type": "bearer"
//  	}
// 

Chilkat.JsonObject jResponse = new Chilkat.JsonObject();
jResponse.EmitCompact = false;
jResponse.Load(jsonResponse);

if (rest.ResponseStatusCode != 200) {
    Debug.WriteLine(jResponse.Emit());
    Debug.WriteLine("Failed.");
    return;
}

//  Get the access token:
string accessToken = jResponse.StringOf("access_token");
Debug.WriteLine("Access token, valid for 60 minutes: " + accessToken);