core: Simplisafe invalid credentials provided

Home Assistant release with the issue:

Last working Home Assistant release (if known): .83

Operating environment (Hass.io/Docker/Windows/etc.):

Docker Component/platform:

https://www.home-assistant.io/components/simplisafe/

Description of problem: I’m getting an “invalid credentials provided” in the log and my control panel isn’t showing up as expected. For debugging purposes, I used my username and password to log into Simplisafe’s site directly without a problem. I’m also using a “+” symbol in my email address if that helps with debugging.

Problem-relevant configuration.yaml entries and (fill out even if it seems unimportant):

simplisafe:
  accounts:
    - username: !secret simplisafe_username
      password: !secret simplisafe_password

Traceback (if applicable):

Additional information: