Hello everyone, I'm new in the comunity

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I have at my disposal a Schneider GTO5310 HMI and a CompactLogix L30ER, and I have to create a system in wich I can set a protected variable with username and password. But, that username must be registered through a STRING to the PLC each time you log in to the HMI and make a chance.
I don't even know where to start, any ideas?
regards
