Decoding and verifying JWT token using System.IdentityModel.Tokens.Jwt
I've been using the JWT library to decode a Json Web Token, and would like to switch to Microsoft's official JWT implementation, System.IdentityModel.Tokens.Jwt.
The documentation is very sparse, so I'm having a hard time figuring how to accomplish what I've been doing with the JWT library. With the JWT library, there is a Decode method that takes the base64 encoded JWT and turns it into JSON which can then be deserialized. I'd like to do something similar using System.IdentityModel.Tokens.Jwt, but after a fair amount of digging, cannot figure out how.
For what it's worth, I'm reading the JWT token from a cookie, for use with Google's identity framework.
Any help would be appreciated.
Answer
Within the package there is a class called JwtSecurityTokenHandler which derives from System.IdentityModel.Tokens.SecurityTokenHandler. In WIF this is the core class for deserialising and serialising security tokens.
The class has a ReadToken(String) method that will take your base64 encoded JWT string and returns a SecurityToken which represents the JWT.
The SecurityTokenHandler also has a ValidateToken(SecurityToken) method which takes your SecurityToken and creates a ReadOnlyCollection<ClaimsIdentity>. Usually for JWT, this will contain a single ClaimsIdentity object that has a set of claims representing the properties of the original JWT.
JwtSecurityTokenHandler defines some additional overloads for ValidateToken, in particular, it has a ClaimsPrincipal ValidateToken(JwtSecurityToken, TokenValidationParameters) overload. The TokenValidationParameters argument allows you to specify the token signing certificate (as a list of X509SecurityTokens). It also has an overload that takes the JWT as a string rather than a SecurityToken.
The code to do this is rather complicated, but can be found in the Global.asax.cx code (TokenValidationHandler class) in the developer sample called "ADAL - Native App to REST service - Authentication with ACS via Browser Dialog", located at
http://code.msdn.microsoft.com/AAL-Native-App-to-REST-de57f2cc
Alternatively, the JwtSecurityToken class has additional methods that are not on the base SecurityToken class, such as a Claims property that gets the contained claims without going via the ClaimsIdentity collection. It also has a Payload property that returns a JwtPayload object that lets you get at the raw JSON of the token. It depends on your scenario which approach it most appropriate.
The general (i.e. non JWT specific) documentation for the SecurityTokenHandler class is at
http://msdn.microsoft.com/en-us/library/system.identitymodel.tokens.securitytokenhandler.aspx
Depending on your application, you can configure the JWT handler into the WIF pipeline exactly like any other handler.
There are 3 samples of it in use in different types of application at
Probably, one will suite your needs or at least be adaptable to them.