@ThongPham
There is no such thing as a permanent Bearer token. How long a Bearer token stays valid is set in the provider that issuing that bearer token. In you case the ldap-provider. Also keep in mind that a bearer token is issued by a specific node in the NiFi cluster and can not be used to authenticate with every node in the NiFi cluster.
Since a secured NiFi will always attempt mutual TLS authentication first. I suggest you instead you generate and use a client certificate to interact with the NiFi API. Mutual TLS based authentication does not use bearer tokens and the authentication will be successful until that client certificate expires which is configurable when generating the certificate. But generally speaking certificates are often valid for 12 or months. Since there is no bearer token, a client certificate can be used with any node in the cluster.
Your other option is to build a flow within your NiFi to get a new bearer token automatically and store that token in maybe a distributedMapCache. Then in your other flow you fetch that bearer token before calling the rest-api endpoint. A failure should loop back to the FetchDistrubutedMapCache just in case you have a scenario where the bearer token expires between fetch and call.
Out of curiosity, what rest-api endpoint are you calling every 20 seconds and why?
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Thank you,
Matt
