fix(inputs.opcua): Fix opcua and opcua-listener for servers using password-based auth

[vsinha]

The Gopcua/opcua client was never properly initialized, which meant that authentication to the opcua server was never configured. My guess is this got lost in the shuffle of the addition of the opcua_listener plugin.

In testing before this change, without calling init, the server gave an error like

2023-01-20T20:27:06Z E! [inputs.opcua] Error in plugin: error in Client Connection: The user identity token is not valid. StatusBadIdentityTokenInvalid (0x80200000)

After Init(), the plugin works and is able to ingest data as expected.

[vsinha]

@LarsStegman does this look right to you? There's a few layers of abstraction and several different things called Init in the telegraf codebase, but it looks like OpcUAClient.Init is specifically configuring options (and not eg starting a subscription), and further on telegraf/plugins/common/opcua/client.go:74 the log line even claims to be initializing OpcUAClient and sets some other state inside the struct.

[LarsStegman]

Hi,

yeah this looks right. Thanks! Looks like it fell through the cracks during the refactor.

Interesting we got no bug reports for this. Maybe almost everybody is using it without the auth part.

Could you look into adding a test for this? I'm not sure if the test container with the OPC server also supports a config with authentication required.

[vsinha]

@LarsStegman done!

Took some digging around in how open62541 is structured but happily they have a binary packaged in the existing docker container which sets itself up with password auth.

[powersj]

Thanks for taking the time to put up a PR!

[srebhan]

Thanks for your fix @vsinha. I have one comment regarding the placement of the call to Init(). Furthermore, I would prefer to split this PR into the fix, which is the missing call to Init() AFAICS, and the cleanup of the test and read_client.
What do you think?

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mips.deb	riscv64.rpm	linux_amd64.tar.gz
mipsel.deb	s390x.rpm	linux_arm64.tar.gz
ppc64el.deb	x86_64.rpm	linux_armel.tar.gz
riscv64.deb		linux_armhf.tar.gz
s390x.deb		linux_i386.tar.gz
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		linux_ppc64le.tar.gz
		linux_riscv64.tar.gz
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		static_linux_amd64.tar.gz

[vsinha]

I made these changes and split out the refactor for a future PR! Thanks for the feedback @srebhan

[srebhan]

Thanks for the nice fix and the splitting @vsinha! @powersj can you please take another look and merge if you agree to the changes made!