OAuth/OIDC Authentication (SASL/OAUTHBEARER)

SASL/OAUTHBEARER enables OAuth 2.0 and OpenID Connect (OIDC) authentication for Kafka. It integrates with cloud identity providers like Azure AD, Okta, Auth0, and Keycloak.

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Overview

When to Use OAuth

Use Case	Recommendation
Cloud-native deployments	Recommended
Azure AD / Entra ID integration	Recommended
Okta / Auth0 / Keycloak	Recommended
Microservices architecture	Recommended
No existing identity provider	Consider SCRAM
On-premises without IdP	Consider Kerberos or SCRAM

OAuth Benefits

Feature	Benefit
Token-based	Short-lived, automatically refreshed
Centralized identity	Single source of truth
Fine-grained scopes	Permission control via claims
No password storage	Tokens from IdP only
Standard protocol	Broad tooling support

Version Requirements

Feature	Kafka Version
SASL/OAUTHBEARER (custom callback)	2.0.0+
Built-in OIDC support	3.1.0+
Token refresh without reconnect	2.2.0+
jwt-bearer grant type	4.1.0+ (KIP-1139)
private_key_jwt client assertion	4.3.0+ (KAFKA-18608)

Kafka 4.3+ private_key_jwt

Kafka 4.3 adds support for the private_key_jwt client authentication method in the OAuth2 client. The client signs an assertion JWT with its private key, removing the need to embed a client secret in configuration. This is the same client authentication mechanism described in RFC 7523 §2.2 and is the recommended approach for production deployments against IdPs that support it.

Use Kafka 3.1+ for OIDC

Kafka 3.1 introduced built-in OIDC support with OAuthBearerLoginCallbackHandler. Earlier versions require custom callback implementation.

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OAuth Flow

Key concepts:

• Access Token - JWT containing identity and claims
• Client Credentials - Application identity (client_id/secret)
• Token Refresh - Automatic renewal before expiry
• Claims - Identity attributes (username, groups, scopes)

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Identity Provider Set up

Azure AD / Entra ID

1. Register application:

Azure Portal -> Azure Active Directory -> App Registrations -> New Registration

Name: kafka-cluster
Account types: Single tenant

1. Configure API permissions:

API Permissions -> Add permission -> APIs my organization uses
Select your Kafka app -> Add permissions

1. Create client secret:

Certificates & secrets -> New client secret
Note: Copy secret value immediately, shown only once

1. Get endpoints:

Token endpoint: https://login.microsoftonline.com/{tenant-id}/oauth2/v2.0/token
JWKS URI: https://login.microsoftonline.com/{tenant-id}/discovery/v2.0/keys

Okta

1. Create application:

Applications -> Create App Integration
Sign-in method: OIDC
Application type: Service (Machine-to-Machine)

1. Configure:

Client authentication: Client secret
Grant type: Client Credentials

1. Get endpoints:

Token endpoint: https://{your-domain}.okta.com/oauth2/default/v1/token
JWKS URI: https://{your-domain}.okta.com/oauth2/default/v1/keys

Keycloak

1. Create client:

Clients -> Create Client
Client ID: kafka-broker
Client authentication: ON
Authentication flow: Service accounts roles

1. Get endpoints:

Token endpoint: https://{keycloak}/realms/{realm}/protocol/openid-connect/token
JWKS URI: https://{keycloak}/realms/{realm}/protocol/openid-connect/certs

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Broker Configuration (Kafka 3.1+)

Basic OIDC Set up

# server.properties

# Listener configuration
listeners=SASL_SSL://0.0.0.0:9093
advertised.listeners=SASL_SSL://kafka1.example.com:9093

# Security protocol
security.inter.broker.protocol=SASL_SSL
sasl.mechanism.inter.broker.protocol=OAUTHBEARER

# Enable OAuth
sasl.enabled.mechanisms=OAUTHBEARER

# OIDC configuration
listener.name.sasl_ssl.oauthbearer.sasl.jaas.config=\
  org.apache.kafka.common.security.oauthbearer.OAuthBearerLoginModule required \
  clientId="kafka-broker" \
  clientSecret="${OAUTH_CLIENT_SECRET}" \
  scope="kafka" ;

# Server callback handler (validates incoming tokens)
listener.name.sasl_ssl.oauthbearer.sasl.server.callback.handler.class=\
  org.apache.kafka.common.security.oauthbearer.secured.OAuthBearerValidatorCallbackHandler

# Login callback handler (obtains tokens for inter-broker)
listener.name.sasl_ssl.oauthbearer.sasl.login.callback.handler.class=\
  org.apache.kafka.common.security.oauthbearer.secured.OAuthBearerLoginCallbackHandler

# OIDC discovery
sasl.oauthbearer.token.endpoint.url=https://login.microsoftonline.com/{tenant}/oauth2/v2.0/token
sasl.oauthbearer.jwks.endpoint.url=https://login.microsoftonline.com/{tenant}/discovery/v2.0/keys

# Expected audience (your Kafka app's client ID)
sasl.oauthbearer.expected.audience=api://kafka-cluster

# Clock skew tolerance (seconds)
sasl.oauthbearer.clock.skew.seconds=30

TLS Configuration

# SSL settings
ssl.keystore.type=PKCS12
ssl.keystore.location=/etc/kafka/ssl/kafka.keystore.p12
ssl.keystore.password=${KEYSTORE_PASSWORD}
ssl.key.password=${KEY_PASSWORD}

ssl.truststore.type=PKCS12
ssl.truststore.location=/etc/kafka/ssl/kafka.truststore.p12
ssl.truststore.password=${TRUSTSTORE_PASSWORD}

ssl.enabled.protocols=TLSv1.3,TLSv1.2
ssl.endpoint.identification.algorithm=HTTPS

Azure AD Configuration

# Azure AD specific
listener.name.sasl_ssl.oauthbearer.sasl.jaas.config=\
  org.apache.kafka.common.security.oauthbearer.OAuthBearerLoginModule required \
  clientId="${AZURE_CLIENT_ID}" \
  clientSecret="${AZURE_CLIENT_SECRET}" \
  scope="api://kafka-cluster/.default" ;

sasl.oauthbearer.token.endpoint.url=https://login.microsoftonline.com/${AZURE_TENANT_ID}/oauth2/v2.0/token
sasl.oauthbearer.jwks.endpoint.url=https://login.microsoftonline.com/${AZURE_TENANT_ID}/discovery/v2.0/keys
sasl.oauthbearer.expected.audience=api://kafka-cluster
sasl.oauthbearer.expected.issuer=https://sts.windows.net/${AZURE_TENANT_ID}/

Okta Configuration

# Okta specific
listener.name.sasl_ssl.oauthbearer.sasl.jaas.config=\
  org.apache.kafka.common.security.oauthbearer.OAuthBearerLoginModule required \
  clientId="${OKTA_CLIENT_ID}" \
  clientSecret="${OKTA_CLIENT_SECRET}" \
  scope="kafka" ;

sasl.oauthbearer.token.endpoint.url=https://${OKTA_DOMAIN}/oauth2/default/v1/token
sasl.oauthbearer.jwks.endpoint.url=https://${OKTA_DOMAIN}/oauth2/default/v1/keys
sasl.oauthbearer.expected.audience=api://default
sasl.oauthbearer.expected.issuer=https://${OKTA_DOMAIN}/oauth2/default

Keycloak Configuration

# Keycloak specific
listener.name.sasl_ssl.oauthbearer.sasl.jaas.config=\
  org.apache.kafka.common.security.oauthbearer.OAuthBearerLoginModule required \
  clientId="${KEYCLOAK_CLIENT_ID}" \
  clientSecret="${KEYCLOAK_CLIENT_SECRET}" \
  scope="openid kafka" ;

sasl.oauthbearer.token.endpoint.url=https://${KEYCLOAK_HOST}/realms/${REALM}/protocol/openid-connect/token
sasl.oauthbearer.jwks.endpoint.url=https://${KEYCLOAK_HOST}/realms/${REALM}/protocol/openid-connect/certs
sasl.oauthbearer.expected.audience=${KEYCLOAK_CLIENT_ID}
sasl.oauthbearer.expected.issuer=https://${KEYCLOAK_HOST}/realms/${REALM}

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Principal Extraction

Extract user identity from JWT claims for authorization:

Claim Mapping

# Extract principal from specific claim
sasl.oauthbearer.sub.claim.name=preferred_username

# Or use multiple claims
# Default: uses 'sub' claim

Claim	Description	Example
sub	Subject (default)	UUID or email
preferred_username	Human-readable username	[email protected]
email	Email address	[email protected]
azp	Authorized party	client_id

Group-Based Authorization

# Extract groups from token
sasl.oauthbearer.groups.claim.name=groups

# Maps to Kafka principals for ACLs
# Group claim: ["kafka-admins", "kafka-producers"]
# Results in User:alice being member of groups

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Client Configuration

Java Client (Kafka 3.1+)

import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.ProducerConfig;
import java.util.Properties;

Properties props = new Properties();
props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "kafka1:9093,kafka2:9093");
props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);

// Security configuration
props.put("security.protocol", "SASL_SSL");
props.put("sasl.mechanism", "OAUTHBEARER");

// OIDC configuration
props.put("sasl.jaas.config",
    "org.apache.kafka.common.security.oauthbearer.OAuthBearerLoginModule required " +
    "clientId=\"my-application\" " +
    "clientSecret=\"" + System.getenv("OAUTH_CLIENT_SECRET") + "\" " +
    "scope=\"kafka\";");

props.put("sasl.login.callback.handler.class",
    "org.apache.kafka.common.security.oauthbearer.secured.OAuthBearerLoginCallbackHandler");

props.put("sasl.oauthbearer.token.endpoint.url",
    "https://login.microsoftonline.com/{tenant}/oauth2/v2.0/token");

// TLS configuration
props.put("ssl.truststore.location", "/etc/kafka/ssl/client.truststore.p12");
props.put("ssl.truststore.password", "truststore-password");
props.put("ssl.truststore.type", "PKCS12");

KafkaProducer<String, String> producer = new KafkaProducer<>(props);

Spring Boot

application.yml:

spring:
  kafka:
    bootstrap-servers: kafka1:9093,kafka2:9093
    properties:
      security.protocol: SASL_SSL
      sasl.mechanism: OAUTHBEARER
      sasl.jaas.config: >
        org.apache.kafka.common.security.oauthbearer.OAuthBearerLoginModule required
        clientId="${OAUTH_CLIENT_ID}"
        clientSecret="${OAUTH_CLIENT_SECRET}"
        scope="kafka";
      sasl.login.callback.handler.class: org.apache.kafka.common.security.oauthbearer.secured.OAuthBearerLoginCallbackHandler
      sasl.oauthbearer.token.endpoint.url: ${OAUTH_TOKEN_ENDPOINT}
    ssl:
      trust-store-location: classpath:truststore.p12
      trust-store-password: ${TRUSTSTORE_PASSWORD}
      trust-store-type: PKCS12

Python (confluent-kafka)

from confluent_kafka import Producer
import requests

# Get token from IdP
def get_oauth_token():
    response = requests.post(
        'https://login.microsoftonline.com/{tenant}/oauth2/v2.0/token',
        data={
            'client_id': 'my-application',
            'client_secret': os.environ['OAUTH_CLIENT_SECRET'],
            'grant_type': 'client_credentials',
            'scope': 'api://kafka-cluster/.default'
        }
    )
    return response.json()['access_token']

def oauth_cb(config_str):
    return get_oauth_token(), time.time() + 3600

config = {
    'bootstrap.servers': 'kafka1:9093,kafka2:9093',
    'security.protocol': 'SASL_SSL',
    'sasl.mechanism': 'OAUTHBEARER',
    'oauth_cb': oauth_cb,
    'ssl.ca.location': '/etc/kafka/ssl/ca-cert.pem',
}

producer = Producer(config)

Command-Line Tools

client.properties:

security.protocol=SASL_SSL
sasl.mechanism=OAUTHBEARER
sasl.jaas.config=org.apache.kafka.common.security.oauthbearer.OAuthBearerLoginModule required \
  clientId="admin-tool" \
  clientSecret="${OAUTH_CLIENT_SECRET}" \
  scope="kafka";
sasl.login.callback.handler.class=org.apache.kafka.common.security.oauthbearer.secured.OAuthBearerLoginCallbackHandler
sasl.oauthbearer.token.endpoint.url=https://login.microsoftonline.com/{tenant}/oauth2/v2.0/token
ssl.truststore.location=/etc/kafka/ssl/client.truststore.p12
ssl.truststore.password=truststore-password

kafka-topics.sh --bootstrap-server kafka:9093 \
  --command-config client.properties \
  --list

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Token Refresh

Automatic Refresh

Kafka clients automatically refresh tokens before expiry:

# Client refresh settings
sasl.login.refresh.window.factor=0.8
sasl.login.refresh.window.jitter=0.05
sasl.login.refresh.min.period.seconds=60
sasl.login.refresh.buffer.seconds=5

Property	Default	Description
refresh.window.factor	0.8	Refresh at 80% of token lifetime
refresh.window.jitter	0.05	Random jitter
refresh.min.period.seconds	60	Minimum refresh interval
refresh.buffer.seconds	5	Buffer before expiry

Connection Re-authentication

Enable broker-initiated re-authentication (Kafka 2.2+):

Broker:

# Force re-authentication every hour
connections.max.reauth.ms=3600000

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Custom Callback Handler (Pre-3.1)

For Kafka versions before 3.1 or custom token logic:

Login Callback (Token Acquisition)

import org.apache.kafka.common.security.oauthbearer.OAuthBearerLoginModule;
import org.apache.kafka.common.security.oauthbearer.OAuthBearerTokenCallback;
import javax.security.auth.callback.*;
import javax.security.auth.login.AppConfigurationEntry;
import java.util.*;

public class CustomOAuthLoginCallbackHandler implements AuthenticateCallbackHandler {

    private String tokenEndpoint;
    private String clientId;
    private String clientSecret;

    @Override
    public void configure(Map<String, ?> configs, String saslMechanism,
                          List<AppConfigurationEntry> jaasConfigEntries) {
        // Extract configuration
        this.tokenEndpoint = (String) configs.get("oauth.token.endpoint");
        this.clientId = (String) configs.get("oauth.client.id");
        this.clientSecret = (String) configs.get("oauth.client.secret");
    }

    @Override
    public void handle(Callback[] callbacks) throws UnsupportedCallbackException {
        for (Callback callback : callbacks) {
            if (callback instanceof OAuthBearerTokenCallback) {
                handleTokenCallback((OAuthBearerTokenCallback) callback);
            } else {
                throw new UnsupportedCallbackException(callback);
            }
        }
    }

    private void handleTokenCallback(OAuthBearerTokenCallback callback) {
        // Fetch token from IdP
        String accessToken = fetchAccessToken();

        // Parse JWT and create token
        OAuthBearerToken token = new OAuthBearerTokenImpl(accessToken);
        callback.token(token);
    }

    private String fetchAccessToken() {
        // HTTP POST to token endpoint
        // Return access_token from response
    }

    @Override
    public void close() {}
}

Validator Callback (Token Validation)

public class CustomOAuthValidatorCallbackHandler implements AuthenticateCallbackHandler {

    private String jwksEndpoint;
    private JWKSet jwkSet;

    @Override
    public void configure(Map<String, ?> configs, String saslMechanism,
                          List<AppConfigurationEntry> jaasConfigEntries) {
        this.jwksEndpoint = (String) configs.get("oauth.jwks.endpoint");
        // Fetch JWKS for signature verification
        this.jwkSet = fetchJWKS();
    }

    @Override
    public void handle(Callback[] callbacks) throws UnsupportedCallbackException {
        for (Callback callback : callbacks) {
            if (callback instanceof OAuthBearerValidatorCallback) {
                handleValidatorCallback((OAuthBearerValidatorCallback) callback);
            } else {
                throw new UnsupportedCallbackException(callback);
            }
        }
    }

    private void handleValidatorCallback(OAuthBearerValidatorCallback callback) {
        String tokenValue = callback.tokenValue();

        // Validate JWT signature using JWKS
        // Validate expiration, audience, issuer
        // Extract claims

        if (isValid(tokenValue)) {
            callback.token(new OAuthBearerTokenImpl(tokenValue));
        } else {
            callback.error("invalid_token", "Token validation failed", null);
        }
    }

    @Override
    public void close() {}
}

Register Custom Handlers

# Broker
listener.name.sasl_ssl.oauthbearer.sasl.server.callback.handler.class=\
  com.example.CustomOAuthValidatorCallbackHandler
listener.name.sasl_ssl.oauthbearer.sasl.login.callback.handler.class=\
  com.example.CustomOAuthLoginCallbackHandler

# Client
sasl.login.callback.handler.class=com.example.CustomOAuthLoginCallbackHandler

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Security Best Practices

Token Security

Best Practice	Description
Short-lived tokens	Use tokens with 1 hour or less lifetime
Secure client secrets	Store in secrets manager, not config files
Validate all claims	Audience, issuer, expiration
Use TLS	Always SASL_SSL, never SASL_PLAINTEXT
Least privilege scopes	Request only needed permissions

Client Secret Management

Environment variables:

export OAUTH_CLIENT_SECRET=$(vault kv get -field=secret secret/kafka/oauth)

Kubernetes secrets:

apiVersion: v1
kind: Secret
metadata:
  name: kafka-oauth
type: Opaque
stringData:
  client-secret: your-client-secret
---
apiVersion: apps/v1
kind: Deployment
spec:
  template:
    spec:
      containers:
        - name: kafka
          env:
            - name: OAUTH_CLIENT_SECRET
              valueFrom:
                secretKeyRef:
                  name: kafka-oauth
                  key: client-secret

Network Security

# HTTPS for all OAuth endpoints
sasl.oauthbearer.token.endpoint.url=https://...
sasl.oauthbearer.jwks.endpoint.url=https://...

# TLS for Kafka
ssl.endpoint.identification.algorithm=HTTPS

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Troubleshooting

Common Errors

Error	Cause	Solution
invalid_token	Expired or malformed token	Check token expiry, IdP config
invalid_client	Wrong client credentials	Verify client_id/secret
invalid_scope	Requested scope not granted	Check IdP permission config
Token validation failed	Signature verification failed	Check JWKS endpoint, clock skew
Connection refused	Cannot reach IdP	Check network, firewall

Debug Logging

Broker:

# log4j.properties
log4j.logger.org.apache.kafka.common.security.oauthbearer=DEBUG
log4j.logger.org.apache.kafka.common.security=DEBUG

Client:

props.put("sasl.login.connect.timeout.ms", "10000");
// Enable DEBUG logging in log4j/logback

Test Token Acquisition

# Test token endpoint directly
curl -X POST https://login.microsoftonline.com/{tenant}/oauth2/v2.0/token \
  -d "client_id={client_id}" \
  -d "client_secret={client_secret}" \
  -d "grant_type=client_credentials" \
  -d "scope=api://kafka-cluster/.default"

# Decode JWT
echo $TOKEN | cut -d'.' -f2 | base64 -d | jq .

Verify JWKS Endpoint

# Fetch JWKS
curl https://login.microsoftonline.com/{tenant}/discovery/v2.0/keys | jq .

Check Clock Synchronization

OAuth tokens are time-sensitive:

# Check time
date
timedatectl status

# Compare with IdP
curl -I https://login.microsoftonline.com | grep Date

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Related Documentation

• Authentication Overview - Mechanism comparison
• SASL/SCRAM - Password-based authentication
• Delegation Tokens - Lightweight tokens
• Authorization - ACL configuration
• Encryption - TLS setup