Prevent passing an array as login

[snipe]

Someone was faffing around on the demo, injecting additional username fields, causing a 500. While they were clearly trying (unsuccessfully) to test for exploits, it was lighting up our rollbar and was annoying. This solves that.

[what-the-diff]

PR Summary

• Enhancement on Login Validation
  Additional validation has been added to the 'username' and 'password' fields in the login control mechanism. This will ensure that only appropriate data types are entered, enhancing the security and reliability of the login process.

• Improved Field Labels
  Visual updates have been made to the labels for 'username' and 'password' fields in the login. Icons have been added to these labels for a better user interface and more intuitive interaction.

• Remember Me functionality
  A new 'Remember Me' feature has been incorporated into the login process. With this, users have the option to stay signed in, increasing ease of access for frequent users.