Do I have to provide my bank identifier without knowing what I am logging into?
No, you don’t. A signature invitation contains a link and a password that enable you to see the content of the document to be signed. The invitation also includes information about who is requesting your signature, what the document’s name is, and there can also be a message with more information.
You can take your time to read the document, and only when you are certain that the document has been addressed specifically to yourself, will you enter your bank ID for the signature.