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Because the HTTP call made to the OAuth/OIDC provider may time out or transiently fail, there will be a retry mechanism that waits between attempts. The number of attempts that are made (including the first attempt) are variable as it uses an exponential backoff approach; the first attempt to connect to the HTTP endpoint will be made immediately. If that first attempt fails, a second attempt will first wait a configurable number of milliseconds–loginRetryBackoffMs–sasl.login.retry.backoff.ms–before trying again. If that second attempt fails, the wait time (loginRetryBackoffMs) will be doubled before a third attempt. This pattern repeats as needed up to the maximum of loginRetryMaxBackoffMswait time of of sasl.login.retry.backoff.max.ms.

There are several configuration options for this callback handler. Sensitive configuration options and SASL extensions appear under the JAAS configuration (sasl.jaas.config) while the rest are top-level configuration.

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• sasl.oauthbearer.token.endpoint.uriurl: OAuth issuer token endpoint URIURL
• sasl.oauthbearer.scope.claim.name: optional override name of the scope claim; defaults to scope
• sasl.oauthbearer.sub.claim.name: optional override name of the sub claim; defaults to sub
• sasl.login.connect.timeout.ms: optional value in milliseconds for HTTPS connect timeout; defaults to 10000
• sasl.login.read.timeout.ms: optional value in milliseconds for HTTPS read timeout; defaults to 10000
• sasl.login.retry.backoff.ms: optional value in milliseconds for the amount of time to wait between HTTPS call attempts; defaults to 100
• sasl.login.retry.backoff.max.backoff.ms: optional value in milliseconds for the maximum wait for HTTPS call attempts (as described above); defaults to 10000

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sasl.login.callback.handler.class=...OAuthBearerLoginCallbackHandler
sasl.login.connect.timeout.ms=15000
sasl.oauthbearer.token.endpoint.uriurl=https://myidp.example.com/oauth2/default/v1/token
sasl.jaas.config=...OAuthBearerLoginModule required \
clientId="abc123" \
clientSecret="S3cr3t!" \
scope="sales-pipeline" \
extension_organizationId="sales-emea" ;

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In the above example, the OAuth provider’s sasl.oauthbearer.token.endpoint.uriurl has been specified as well as an override of the default for sasl.login.connect.timeout.ms. The values for clientId and clientSecret as provided by the OAuth provider for an “API” or “machine-to-machine” account are required in the JAAS configuration. The optional scope value will allow the inclusion of a scope parameter when requesting the token.

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• sasl.oauthbearer.jwks.endpoint.uriurl: OAuth issuer's JWK Set endpoint URI from URL from which to retrieve the set of JWKs managed by the provider; this can be a file://-based URL that points to a broker file system-accessible file-based copy of the JWKS data. This allows the JWKS data to be updated on the file system and refreshed on the broker when the file is updated, thus avoiding any HTTP(S) communication with the OAuth/OIDC provider

• sasl.oauthbearer.jwks.refresh.interval.ms: optional value in milliseconds for how often to refresh the JWKS from the URL pointed to by sasl.oauthbearer.jwks.endpoint.uriurl. Only used when using an HTTP(S)-based URI URL for sasl.oauthbearer.jwks.endpoint.uriurl. Defaults to 3600000 (1 hour)

• sasl.oauthbearer.sub.claim.name: name of the scope from which to extract the subject claim from the JWT; defaults to sub

• sasl.oauthbearer.scope.claim.name: name of the scope from which to extract the scope claim from the JWT; defaults to scope

• sasl.oauthbearer.clock.skew.seconds: optional value in seconds for the clock skew between the OAuth/OIDC provider and the broker. Only used when using an HTTP(S)-based URI URL for sasl.oauthbearer.jwks.endpoint.uriurl. Defaults to 30
• sasl.oauthbearer.expected.audience: The (optional) comma-delimited setting for the broker to use to verify that the JWT was issued for one of the expected audiences. The JWT will be inspected for the standard OAuth aud claim and if this configuration option is set, the broker will match the value from JWT's aud claim to see if there is an exact match. If there is no match, the broker will reject the JWT and authentication will fail.
• sasl.oauthbearer.expected.issuer: Optional setting for the broker to use to verify that the JWT was created by the expected issuer. The JWT will be inspected for the standard OAuth iss claim and if this configuration option is set, the broker will match the value from JWT's iss claim to see if there is an exact match. If there is no match, the broker will reject the JWT and authentication will fail.

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listener.name.<listener name>.oauthbearer.sasl.login.callback.handler.class=...OAuthBearerValidatorCallbackHandler
listener.name.<listener name>.oauthbearer.sasl.jaas.config=...OAuthBearerLoginModule required;
sasl.oauthbearer.jwks.endpoint.uriurl=https://myidp.example.com/oauth2/default/v1/keys
sasl.oauthbearer.scope.claim.name=scp

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In the above configuration the broker points to the appropriate OAuth provider sasl.oauthbearer.jwks.endpoint.uriurl to retrieve a the set of JWKs for validation. In this example, a non-default value for sasl.oauthbearer.scope.claim.name has been provided because the provider uses scp for the name of the scope claim in the JWT it produces.

JWKS Management Logic

JSON Web Key Set (JWKS) is a JSON document that lists the keys by which the OAuth/OIDC provider has signed the JWT.

Here is a sample JWKS JSON document:

{
  "keys": [
    {
      "kty": "RSA",
      "alg": "RS256",
      "kid": "abc123",
      "use": "sig",
      "e": "AQAB",
      "n": "..."
    },
    {
      "kty": "RSA",
      "alg": "RS256",
      "kid": "def456",
      "use": "sig",
      "e": "AQAB",
      "n": "..."
    }
  ]
}

Without going into too much detail, the array of keys enumerates the key data that the provider is using to sign the JWT signature. The key ID (kid) is referenced by the JWT's header in order to match up the JWT's signing key with the key in the JWKS. During the validation step, the jose4j OAuth library will use the contents of the appropriate key in the JWKS to validate the signature.

Given that the JWKS is referenced by the JWT, the JWKS must be made available by the OAuth/OIDC provider so that a JWT can be validated.

The JWKS will The JWKS will be kept up-to-date in two main ways:

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1. If the JWKS URL is HTTP(S)-based and if the broker hasn't already attempted to resolve the key ID, enqueue a background thread to reload the JWKS from the HTTP(S) endpoint. The broker will keep track of key ID resolution failures so it doesn't repeatedly attempt to do so. If the JWKS URL is file://-based, no remediatory remediation processing will occur.
2. Send an authentication failure to the client. Since it is unknown at this point in processing of the key ID is valid-but-missing or if the key ID is just invalid, the broker will always issue an authentication error. Between the authentication failure delay mechanism and any client retry, there may be sufficient time for the broker to update the JWKS.

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./bin/kafka-run-class.sh org.apache.kafka.tools.OAuthCompatibilityTool \
  --client-id foo \
  --client-secret bar \
  --token-endpoint-uriurl https://example.com/oauth2/v1/token \
  --jwks-endpoint-uriurl https://example.com/oauth2/v1/keys

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