corvid login

Hello Everybody
I need some advices (or examples) to write some lines of code using Corvid.
Basically I need to allow the User to subscribe (sign in) in the site, using a database’s query that works ONLY if the content of the textbox is already present in the database.
I can already work with c# and c++, so I understand the language but can’t really write the code itself.
If anybody could help me with some examples or anything else I’d be so grateful.
Thank y’all in advance!

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