Solution:

https://github.com/apache/nifi

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Authenticating

The default configuration generates a random username and password on startup. NiFi writes the generated credentials to the application log located in logs/nifi-app.log under the NiFi installation directory.

The following command can be used to find the generated credentials on operating systems with grep installed:

laptop:nifi-1.0.0-SNAPSHOT myuser$ grep Generated logs/nifi-app*log

NiFi logs the generated credentials as follows:

Generated Username [USERNAME]
Generated Password [PASSWORD]

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File Explorer > Nifi Folder > "logs" Folder > Edit "nifi-app.log" > Search "Generated Username"