In order to successfully establish a connection to the Broker, the connection must be authenticated. The Broker supports a number of different authentication schemes, each with its own "authentication provider". Any number of Authentication Providers can be configured on the Broker at the same time. Only unused Authentication Provider can be deleted. For delete requests attempting to delete Authentication Provider associated with the Ports, the errors will be returned and delete operations will be aborted. It is possible to change the Authentication Provider on Port at runtime. However, the Broker restart is required for changes on Port to take effect. Authentication Providers may choose to selectively disable certain authentication mechanisms depending on whether an encrypted transport is being used or not. This is to avoid insecure configurations. Notably, by default the PLAIN mechanism will be disabled on non-SSL connections. This security feature can be overwritten by setting secureOnlyMechanisms = [] in the authentication provider section of the config.json. Changing the secureOnlyMechanism is a breach of security and might cause passwords to be transfered in the clear. Use at your own risk!