With the rise of Kotlin as a first-class language for developing Android apps, it's no surprise that more and more developers are interested in using Kotlin for server-side development as well. In this article, we'll take a look at how to use Kotlin and the Java Web Tokens (JWT) framework to secure a RESTful API.
JWT is a standard for creating access tokens that allow servers to verify the identity of clients. This is especially important in a RESTful API, where clients can be anything from a mobile app to a browser extension. By using JWT, we can be sure that only authorized clients can access our API.
To use JWT with Kotlin, we'll need to install the kotlin-jwt library. This library provides a set of functions for creating and verifying JWT tokens.
Once we have the kotlin-jwt library installed, we can use it to create a JWT token like this:
val jwt = JWT.create()
.withSubject("user@example.com")
.withExpiresAt(Date())
.sign(algorithm)
where algorithm
is an instance of Algorithm
that specifies the signing algorithm to use. For example, we could use the HMAC256
algorithm like this:
val algorithm = Algorithm.HMAC256("secret")
We can then use the jwt
variable to generate a token:
val token = jwt.generate()
Now that we have a token, we can use it to secure our API. For example, we can add it to the Authorization
header of our HTTP requests:
val request = Request.Builder()
.url("https://example.com/api/v1/users")
.header("Authorization", "Bearer $token")
.build()
The server can then use the verify
function to verify the token:
val jwt = JWT.require(algorithm)
.build()
val verifiedToken = jwt.verify(token)
If the token is valid, the verifiedToken
variable will contain the decoded token. We can then use the getSubject
function to get the user's email address:
val userEmail = verifiedToken.getSubject()
Now that we know how to use Kotlin and JWT to secure a RESTful API, let's look at some resources for further reading.