For security reasons any sensitive data should be encrypted when being passed between the web server and application server.
The most common example for encryption is of course a password. Here is an example detailing how you may implement encryption and decryption.
1. Start by creating a field to store your encryption value (You can store this value wherever you like but a field does the job nicely)
2. In your Web Page or Reusable Part encrypt the value entered by the user like this:
* Use default value for encryption
#XSPasswordEncrypted := #XSPassword.Encrypt( #XSEncryptKey )
3. Now you can pass the encrypted value to a Server module securely, where it can be verified or saved.
An equivalent decrypt intrinsic is available.