Failed to decode authentication header – How to solve this Elasticsearch error

Opster Team

Aug-23, Version: 8.5-8.9

Briefly, this error occurs when Elasticsearch is unable to decode the authentication header due to incorrect formatting or encoding. This could be due to an incorrect username/password combination, or a problem with the Base64 encoding of the credentials. To resolve this issue, ensure that the credentials are correct and properly formatted. If using Base64 encoding, verify that it’s done correctly. Also, check the Elasticsearch security settings to ensure that the correct authentication method is being used.

This guide will help you check for common problems that cause the log ” Failed to decode authentication [” + header + “] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: plugin.

Log Context

Log “Failed to decode authentication [” + header + “]” classname is
We extracted the following from Elasticsearch source code for those seeking an in-depth context :

            StreamInput input = StreamInput.wrap(bytes);
            TransportVersion version = TransportVersion.readVersion(input);
            return new Authentication(input);
        } catch (IOException | RuntimeException e) {
            logger.warn("Failed to decode authentication [" + header + "]"; e);
            throw e;

    public Authentication getAuthentication(ThreadContext context) {