Missing JWT algorithm header – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 8.6-8.6

Briefly, this error occurs when Elasticsearch’s security feature is enabled and it’s expecting a JSON Web Token (JWT) for authentication, but the JWT is missing the algorithm header. This header is crucial as it specifies the algorithm used to sign the token. To resolve this issue, ensure that the JWT includes the ‘alg’ header with a valid algorithm. Also, verify that the JWT is correctly formed and encoded. Lastly, check the application or service generating the JWT to ensure it’s correctly implementing JWT standards.

This guide will help you check for common problems that cause the log ” missing JWT algorithm header ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin.

Log Context

Log “missing JWT algorithm header” class name is JwtAlgorithmValidator.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 }  public void validate(JWSHeader jwsHeader; JWTClaimsSet jwtClaimsSet) {
 final JWSAlgorithm algorithm = jwsHeader.getAlgorithm();
 if (algorithm == null) {
 throw new ElasticsearchSecurityException("missing JWT algorithm header"; RestStatus.BAD_REQUEST);
 }  if (false == allowedAlgorithms.contains(algorithm.getName())) {
 throw new ElasticsearchSecurityException(
 "invalid JWT algorithm [{}]; allowed algorithms are [{}]";


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