Hey everyone! Have you ever felt lost in the world of identity management, wishing there was an easier way to understand client credentials? You're not alone! As a developer deeply involved with Keycloak, I set out to explain the client credential grant type. Come along as we explore Keycloak's client credentials, uncovering their secrets and learning how they keep our applications safe. Let's simplify security together!

In this blog, we'll talk about how Keycloak helps to keep your data secure with client credentials.
Keycloak is like a guard for your digital castle, making sure only the right people can get in.

What Are Client Credentials?

Think of client credentials as secret keys that allow different parts of a computer system to talk to each other securely. These keys ensure that only trusted parts of the system can access sensitive information.

Client credential grant types in Keycloak are mechanisms for clients to obtain access tokens without user involvement. These grant types are ideal for machine-to-machine communication scenarios where a client needs to access protected resources directly.

Types of Client Credentials

1. Client Secret (Secret Keys):

Imagine having a special password that only your computer knows. That's what a secret key is. It's used when your computer needs to talk to another computer, proving it's really you.

The client secret grant type involves the client presenting its client ID and client secret to obtain an access token. This is a common method used to authenticate clients securely.

Use: when clients can securely store and transmit a secret.
Suitable for web applications and services running in secure environments.

Generation: To generate a client secret in Keycloak:

    1. Log in to the Keycloak Admin Console.
    2. Go to the Clients section and select the desired client.
    3. Navigate to the Credentials tab.
    4. Click on the Regenerate Secret button to generate a new client secret.

Verification with Curl:

curl -X POST \
    -d "client_id=your_client_id" \
    -d "client_secret=your_client_secret" \
    -d "grant_type=client_credentials" \
    http://keycloak-server/auth/realms/your_realm/protocol/openid-connect/token 

2. JWT Public Key (Signed Codes):

This is like having a secret code that's been stamped with your unique mark. When your computer wants to talk to another one, it shows this code, proving it's genuine.

With the JWT public key grant type, the client presents a JSON Web Token (JWT) signed with its private key. Keycloak verifies the JWT signature using the client's public key and issues an access token if the signature is valid.

Use: Ideal when clients have access to their private keys and can sign JWTs.
Commonly used in scenarios where clients are capable of JWT generation and signing.

Generation: To generate a JWT public key in Keycloak:

    1. Go to the Realm Settings in the Keycloak Admin Console.
    2. Select the Keys tab.
    3. Click on the RSA Key Pair button to generate a new RSA key pair.
    4. The public key will be displayed in the Keycloak Admin Console.

Verification with Curl:

curl -X POST \
    -d "client_id=your_client_id" \
    -d "client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer" \
    -d "client_assertion=your_signed_jwt" \
    -d "grant_type=client_credentials" \
    http://keycloak-server/auth/realms/your_realm/protocol/openid-connect/token

3. X.509 Public Key Certificate (Special Certificates):

These are like having a badge that proves you belong. When your computer wants to talk to another one, it shows its badge, and if it's trusted, it gets access.

This grant type requires the client to present an X.509 public key certificate during token request. Keycloak validates the certificate and issues an access token if the certificate is trusted.

Use: Recommended for environments where certificates can be managed securely.
Provides an additional layer of security by leveraging X.509 certificates for client authentication.

Generation: To generate an X.509 public key certificate in Keycloak:

    1. Obtain or generate an X.509 certificate signed by a trusted certificate authority (CA).
    2. Upload the X.509 certificate to the Keycloak Admin Console under the desired client's Credentials tab.

Verification with Curl:

curl -X POST \
    -d "client_id=your_client_id" \
    -d "client_assertion_type=urn:ietf:params:oauth:client-assertion-type:tls_client_auth" \
    -d "client_assertion=your_client_certificate" \
    -d "grant_type=client_credentials" \
    http://keycloak-server/auth/realms/your_realm/protocol/openid-connect/token

4. Signed JWT (Coded Messages):

Think of this as sending a secret message that only the right person can read. Your computer sends this message, and if it's decoded correctly, it gets access.

In the signed JWT grant type, the client presents a signed JWT without using a client secret. Keycloak verifies the JWT signature and grants access if the signature is valid.

Use: Useful when clients need to generate JWTs but do not have the capability to securely store secrets.
Offers a balance between security and ease of implementation.

Generation: To generate a signed JWT in Keycloak:

    1. Use a JWT library or tool to generate a JWT signed with the client's private key.
    2. Include the signed JWT, client ID, grant type (e.g., client_credentials), and any other required parameters in the request body.

Verification with Curl:

curl -X POST \
-d "client_id=your_client_id" \
-d "client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer" \
-d "client_assertion=your_signed_jwt" \
-d "grant_type=client_credentials" \
http://keycloak-server/auth/realms/your_realm/protocol/openid-connect/token

5. Signed JWT with Client Secret (Secret Messages with Backup):

This is like sending a secret message with an extra lock. Your computer sends the message along with a backup key, just to be extra safe.

This grant type is similar to the signed JWT grant type, but the client also includes its client secret during token request for added security.

Use: Combines the security of signed JWTs with the added protection of a client secret.
Suitable for scenarios where both JWT authentication and client secret authentication are desired.

Generation: To generate a signed JWT with a client secret in Keycloak:

    1. Use a JWT library or tool to generate a JWT signed with the client's private key.
    2. Include the signed JWT, client ID, client secret, grant type (e.g., client_credentials), and any other required parameters in the request body.

Verification with Curl:

curl -X POST \
-d "client_id=your_client_id" \
-d "client_secret=your_client_secret" \
-d "client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer" \
-d "client_assertion=your_signed_jwt" \
-d "grant_type=client_credentials" \
http://keycloak-server/auth/realms/your_realm/protocol/openid-connect/token

Real-Life Scenarios

1. Banking Apps: When you use a banking app on your phone, it talks to the bank's computers to check your account. It does this using a client secret, like a password, to make sure it's really you.

2. Sharing Data: Companies often share data with each other. They use JWT public keys to prove they're not imposters and to keep the data safe from prying eyes.

3. Inside the Bank: Different parts of a bank's computer system need to talk to each other. They use X.509 certificates, like badges, to make sure they're all part of the same team.

4. Microservices: Banks use lots of little programs to handle different tasks. They use signed JWTs, like secret messages, to let these programs talk to each other securely.

5. Partnerships: When banks work with other companies, they need to be extra careful. They use signed JWTs with client secrets, like secret messages with extra locks, to make sure everything stays safe.

Keeping Your Castle Safe

So, why does all this matter? Well, just like you want to keep your real castle safe from intruders, you want to keep your digital castle safe too. Keycloak helps make sure only the right people can get in, keeping your data secure and your digital life protected.

In wrapping up, understanding client credentials in Keycloak is crucial for keeping our applications secure. Stay tuned for more in-depth discussions on each credential type in our upcoming series. By learning more, we can build stronger and safer systems. Keep track and join me as we uncover the secrets of Keycloak, step by step!