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Overview

• This issue pertains to SASL/OAUTHBEARER mechanism of Kafka authentication. 
• Kafka clients can use SASL/OAUTHBEARER  mechanism by overriding the custom call back handlers . 
• KIP-768 available from v3.1  further extends the mechanism with a production grade implementation. 
• Kafka's SASL/OAUTHBEARER  mechanism currently rejects the non-JWT (i.e. opaque) tokens. This is because of a more restrictive set of characters than what RFC-6750 recommends. 
• This JIRA can be considered an extension of KIP-768 to support the opaque tokens as well apart from the JWT tokens.

In summary the following character set should be supported as per the RFC - 

1*( ALPHA / DIGIT /
                       "-" / "." / "_" / "~" / "+" / "/" ) *"="