Support Direct Pasting of PEM Certificates from Clipboard

[yeikel]

Is your feature request related to a problem? Please describe.
I frequently receive certificates in PEM format via direct messages (for example, through Slack)

Although the tool provides an “Examine System Clipboard” option, it does not allow directly pasting certificate content (e.g., via Ctrl+V / Cmd+V)

Describe the solution you'd like
It would be helpful to allow users to paste PEM-formatted certificate content directly. Supporting standard paste key bindings (Ctrl+V / Cmd+V) would make this workflow faster and more intuitive.

Describe alternatives you've considered
Continue using the existing workflow

• Copy into the clipboard
• Click on the “Examine System Clipboard” button

[kaikramer]

Sounds like a good usability improvement.

However, there are a few points to consider from a project/product view if we add "paste certificate". I'll just do a quick brainstorming:

• First of all if we can paste certificates, then I would also expect to be able to paste keys. For keys it's however a bit more complicated because you need a matching certificate to be able to insert it into a keystore.
• When pasting a certificate always check if there is a key pair in this keystore that matches the public key of the certificate and ask user to replace it?
• Same as above but for certificate chain elements of a key pair entry.
• Should multiple certificates in the clipboard be allowed? Why not?
• What about files in the clipboard? Check if they are certificates (PEM or DER) or keys and also paste them into the keystore?
• What about CSRs? Just ignore it when pasting them or show them (same as "examine clipboard")? Probably better to ignore them.