Support JWT Authentication

[pjgg]

support service authn by JWT.

Documentation:

• https://docs.hivemq.com/ese/4.5/enterprise-security-extension/ese.html

HiveMQ broker (ESE extension) configuration:

<jwt-realm>
    <name>jwt-backend</name> <!-- mandatory -->
    <enabled>true</enabled> <!-- mandatory -->
    <configuration>
        <jwks-endpoint>https://some.uri</jwks-endpoint> <!-- mandatory -->
        <jwks-cache-duration>1800</jwks-cache-duration> <!-- optional, default is 1800 -->
    </configuration>
</jwt-realm>

Expected output:

• Implementation
• End-to-end coverage
• Documentation