Bing's portal can now be accessed using your Bing username and password, or by using your credentials from one of several external identity providers (currently Google, Microsoft, Apple, Paypal). This is often referred to as "Single Sign On" (SSO).
Bing matches the email address from your SSO provider to the Bing user database in order to determine your Bing account and access permissions.
SSO removes the need for you to remember and manage a separate Bing password - a good thing!
Your Bing account may need to be configured to allow the use of SSO. Consult your account administrator, or Bing Customer Service, to arrange for SSO to be enabled.