DEV Community

Roy for BLST

Posted on


How to use JWT to Authenticate Your API

What is JWT?

JWTs are composed of three parts: a header, a payload, and a signature. The header and payload are JSON objects, which are signed using a secret key. The signature is used to verify that the token has not been tampered with.

The header usually looks something like this:

  "alg": "HS256",
  "typ": "JWT"
Enter fullscreen mode Exit fullscreen mode

The "alg" value specifies the algorithm used to sign the token, such as "HMACSHA256" or "RS256". The "typ" value specifies that this is a JSON Web Token.
The payload contains the claims, which are the statements that we want to make about the user. These claims are encoded as JSON objects. Some common claims are "iss" (issuer), "sub" (subject), "exp" (expiration time), and "aud" (audience).

Here is an example payload:

  "iss": "",
  "sub": "jsmith",
  "exp": 1301819380,
  "aud": ""
Enter fullscreen mode Exit fullscreen mode

How JWT Works

In order to create a JSON Web Token, the first step is to create a header that contains the algorithm used to generate the token, as well as the type of token being generated. The header is then encrypted with a secret key, and the resulting string is Base64 encoded. The body of the token is then created, which contains the information to be encrypted. This can be any type of data, but is typically a JSON object. The body is then encrypted with the same secret key used to encrypt the header. Finally, the two encrypted strings are combined and a signature is generated. This signature is used to ensure that the token has not been tampered with, and can be verified by any party that receives the token.

JSON Web Tokens are typically used in authentication procedures, in which a user provides their credentials to a server in order to prove their identity. The server then creates a token containing information about the user, such as their name and email address. This token is then sent back to the user, who can then use it to access resources on the server that they are authorized to access. JSON Web Tokens can also be used in authorization procedures, in which a user receives a token from a trusted party that allows them to access certain resources. For example, a user might receive a token from an organization that allows them to access their website.
JSON Web Tokens are a convenient and secure way to exchange information between parties. They are easy to implement and can be used in many different types of applications.

Advantages of Using JWT

JWT are stateless, which means they can be easily scaled. This is because there is no need to store any session information on the server. JWT are also more secure than other methods of authentication, such as Basic Auth. This is because JWT are signed, which means that they cannot be tampered with. Additionally, JWT are easy to use and implement.

How to Use JWT to Authenticate Your API

In order to create a JSON object containing the claims you want to make, you'll first need to decide what claims you want to make. For example, you might want to include the user's ID, name, and email address. Once you've decided on the claims you want to make, you can use a Json Web Token library to create the JSON object.
Once you have the JSON object, you'll need to sign it using a secret key. The secret key is used to ensure that only you can sign the JSON object. Once you have the signed JSON object, you can then send it to the user.
The user will then need to send the signed JSON object back to you in order to authenticate their identity. You can use a library like jwtsimple to verify the signature of the JSON object. If the signature is valid, then the user is authenticated.
There are a few other things to keep in mind when using JWT for authentication. First, it's important to keep your secret key safe. If someone were to get ahold of your secret key, they could potentially forge signatures and gain access to your API. Second, JWT is intended for use with HTTPS in order to prevent man in the middle attacks. Without HTTPS, an attacker could intercept the signed JSON object and replace it with their own signed object.
JWT is a powerful tool for authenticating users and protecting APIs. By following the steps above, you can ensure that only authorized users have access to your API.


JWT is a standard for creating access tokens that are used to authenticate an API. The tokens are signed with a secret key and can be verified with the public key. JWT is a secure and efficient way to authenticate an API. It is easy to implement and can be used with any programming language.

If you're looking to add an extra layer of security to your API, then using JWT is a great way to do so! Not only will it help to keep your data safe, but it can also be a lot of fun to use. Just make sure to follow the instructions carefully and you'll be up and running in no time.

Star our Github repo and join the discussion in our Discord channel to help us make BLST even better!
Test your API for free now at BLST!

Oldest comments (3)

jiseeeh_6 profile image
JC Camara

Hello, I'm a newbie and what I did was sign the user info when they sign-in or login and then store the token in the local storage

after that, on app mount, i send the token to api/verify to check if it is valid or not, if yes they're already logged in, else they're not.

did my use case just okay?

roy8 profile image

There are a few different ways to handle authentication, and it really depends on your application as to what will work best.
In general, what you've done is a pretty standard approach.

jiseeeh_6 profile image
JC Camara

Thank you!