What is a Bearer Token? A Complete Guide for Developers
In the world of modern web applications and APIs, authentication and authorization mechanisms are critical. Whether you're building a RESTful API, working with OAuth2, or integrating third-party services, you've likely encountered the term "Bearer Token." But what exactly is a bearer token? How does it work? And one of the most common questions: Can you reuse a bearer token?
In this article, we’ll dive deep into bearer tokens — how they work, when to use them, whether you can reuse them, and how platforms like Keploy.io make working with APIs more testable and secure. Let’s break it all down.
What is a Bearer Token?
A Bearer Token is a type of access token used in HTTP authentication. It is part of the OAuth 2.0 authorization framework, which is the industry standard for token-based authentication.
Definition:
A bearer token is a string that a client uses to access a protected resource on a server. The term "bearer" indicates that whoever holds the token (the bearer) can use it to gain access to the associated resources — no further identity proof is required.
Format:
A typical bearer token is a long, opaque string, sometimes encoded in Base64 or JWT (JSON Web Token) format. For example:
Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9
How It Works:
A client (e.g., mobile app or frontend) sends credentials to an authentication server.
The server returns a bearer token upon successful authentication.
The client uses the bearer token in the Authorization header when requesting resources from a resource server.
The server verifies the token and, if valid, grants access.
Benefits of Bearer Tokens
Because of certain advantages, bearer tokens are widely used in the industry.
Stateless: There is no need for the server to remember the user’s session.
It is suited to work with both microservices and serverless architecture.
Cross-domain is perfect for APIs that send responses to mobile, web or any other type of client application.
Secure: Your valuables are protected for only a short time and cannot be understood if stolen.
Can You Reuse a Bearer Token?
The short answer is: Yes, but it depends on the token's lifespan and policy.
Let’s break it down:
1. Reusable Within Validity Period
Bearer tokens are generally reusable as long as they have not expired or been revoked. Most APIs set an expiration time (TTL — Time to Live) for tokens, typically between 15 minutes to a few hours.# Example cURL call using a bearer token curl -H "Authorization: Bearer YOUR_TOKEN_HERE" https://api.example.com/data
As long as YOUR_TOKEN_HERE is valid and not blacklisted, you can reuse it for multiple API calls.
2. Limited Reusability for Security
There are systems that have very strict security policies in place.
Some platforms set up tokens that are designed to be used just one time.
To protect against token theft, the tokens are made to expire after just a few seconds.
Some APIs let you either manually or automatically revoke bearer tokens when they detect possible suspicious activity.
3. Token Reuse in Test Environments
In test environments, reusing bearer tokens can make development easier. However, it's crucial to avoid this practice in production unless you're handling token expiration and renewal securely.
Refresh Tokens vs Bearer Tokens
Bearer tokens are often confused with refresh tokens. Here’s how they differ:
Pros and cons of bearer token
Bearer tokens are useful and have limitations in terms of authentication and authorization.
Pros of Bearer Tokens:
They are user-friendly. The process of using and deploying bearer tokens is simple, so they’re good for developers.
Since statelessness is the norm in bearer tokens, there is no need for a server to hold on to token data. As a result, the server-side development and how the website faces increasing load become simpler.
Because of their flexibility, bearer tokens can handle access to web applications and be part of single sign on (SSO).
If the authentication is done in a centralised way, deleting the access token is a quick way to deal with compromised tokens or stop access.
Cons of Bearer Tokens:
The dependable nature of bearer tokens is closely linked to the security of the way the information is sent (usually HTTPS). If someone gets caught using them, their data can be taken advantage of.
The security risk comes from token theft, since someone who steals it may be able to access resources.
Bearer tokens are mainly defined by carrying a restricted amount of singer or application data. When there isn’t enough information, you might need to ask more questions.
It is important to handle all the bearer token actions such as issuance, renewal and cancelation with the upmost security.
Access Issues are a bit common. Bearer tokens often come with big access scopes which could create security risks if close regulation is not provided.
Best Practices for Using Bearer Tokens
Be sure to use HTTPS when sending bearer tokens.
Bound the tokens given instead of full access: This way, the risk can be lowered.
You can secure your application’s sessions by shortening their life with low TTLs and refresh tokens.
Token Storage:
Mobile/Web Clients: Don’t forget to create secure storage (such as with keychain or secure cookies).
Don’t keep tokens in your log files, only store them in your system's memory.
When a user has logged out or reset the password, the bearer access token should no longer be valid.
Rotation Strategy: Stamp and invalidate tokens after they are used.
Keeping up with the company monitor allows early detection of suspicious token use.
Code Example: Using Bearer Token in a Node.js App
const axios = require('axios'); const API_URL = 'https://api.example.com/user/profile'; const BEARER_TOKEN = 'YOUR_ACCESS_TOKEN'; axios.get(API_URL, { headers: { Authorization: `Bearer ${BEARER_TOKEN}` } }) .then(response => { console.log('User Data:', response.data); }) .catch(error => { console.error('Error:', error); });
Security Risks of Bearer Tokens
1. Token Theft
If a bearer token is intercepted or leaked (e.g., in logs), the attacker can access resources.
2. Replay Attacks
Reusing a token in an unauthorized context can lead to replay attacks.
3. Token Expiry
Clients relying on long-lived tokens may fail if the token expires during a critical operation.
Conclusion
Bearer tokens provide the foundation for today’s API authentication. They are flexible, have no citizenship and are straightforward to deploy, yet they are responsible for security aspects.
In that case, are bearer tokens usable more than one time? If it’s not revoked or has not expired yet, it’s still good. Still, handling storage, use and expiration the right way is important to decrease the risks.
Keploy.io for Secure API Testing
Testing APIs that rely on bearer tokens is one of the toughest problems developers deal with. The short lifespan of tokens means it’s hard to re-run the same tests multiple times.
That’s why tools like Keploy.io are needed.
Keploy allows you to automatically generate cases for testing and mock data, all from your true API traffic. With it, teams can complete all types of testing without the need for manual tests.
Keploy supports:
Capturing bearer tokens from live traffic
Creating test cases with saved headers and tokens
Simulating authenticated requests in test environments
Mocking dependencies like third-party services using bearer token auth
Why It Matters:
Most of the time, when testing APIs using tokens, developers have to set up fake tokens or handle test suite setup on their own. With Keploy, you are able to:
Take actual bearer tokens that are shared in live data traffic.
Repeat token-authenticated functions during the testing phase.
Makes tests for your APIs attainable and realistic.
Use Keploy when working with real software products
Test each authenticated API by creating the necessary test cases automatically.
Make testing go faster by decreasing the amount of manual setup required.
Info from API log files will allow you to see and stop signs of token misuse.
Adding Keploy to your CI/CD steps means your token-based security will be tested and solid — very useful for applications in fintech, healthcare or sensitive data areas.
Further Reading
https://keploy.io/blog/community/how-to-run-pytest-program
https://keploy.io/blog/community/best-claude-3-5-style-for-code
https://keploy.io/blog/community/understanding-json-templatization-with-recursion-for-dynamic-data-handling
FAQ’s
Q1. Can you reuse a bearer token after the user logs out?
Unfortunately, logging out does not always invalidate the token on the backend. In most cases, if the server fails to remove the token from the session, it might still be considered valid.
Q2. Can bearer tokens be shared between clients?
In theory, it’s allowed, but you shouldn’t do it. No one else can provide a token to a client—every client must generate its own. If you share your tokens, you put your system at higher risk of unauthorized use and hacking.
Q3. Are bearer tokens secure?
Bearer tokens are safe to use when you handle them correctly.
Use HTTPS to send information.
Do not place your money where it can be accessed by anyone.
Do not display your values in your URLs.
Set the expiration period for the tokens short and rotate refresh tokens.
Q4. How do I test APIs with bearer tokens?
Use tools like:
Postman: Store token as environment variable
cURL: Pass it in headers
Keploy.io: Automatically capture and replay bearer-token-authenticated calls in test environments
