Looking for logging into the Alternate Id Active Directory site and are not getting the correct working link for it? In such a case, you can use the links given here by searching your desired login page in the search box. If the page is present on our website then you will get all the links related to the Alternate Id Active Directory site. After that you can login as usual with your login credentials.
https://docs.microsoft.com/de-de/windows-server/identity/ad-fs/operations/configuring-alternate-login-id
https://treeforestcloud.wordpress.com/2018/05/27/using-alternate-login-id-without-using-alternate-login-id-part-3/
https://www.mcseboard.de/topic/213565-upn-nachtr%C3%A4glich-%C3%A4ndern-alternative-login-id/
https://www.ibm.com/support/knowledgecenter/en/SSCT62/com.ibm.iamservice.doc/tasks/t_cfg_adfs_email.html
https://blogs.perficient.com/2015/02/24/office-365-the-limitations-of-alternate-login-id/
https://serverfault.com/questions/439361/define-an-alternate-login-domain-for-active-directory
https://community.spiceworks.com/topic/874425-alternate-login-id
https://feedback.azure.com/forums/169401-azure-active-directory/suggestions/34544287-make-azure-mfa-work-on-adfs-when-alternate-login
https://www.linkedin.com/pulse/configure-ad-fs-use-email-address-alternate-login-id-case-ahmad-yasin
https://support.oneidentity.com/authentication-services/kb/18606/how-to-configure-an-alternate-attribute-for-login-or-group-names-what-ad-attribute-for-login-is-being-used-
https://msexperttalk.com/configure-ad-fs-alternate-login-id-office-365/
https://github.com/MicrosoftDocs/azure-docs/blob/master/articles/active-directory/hybrid/how-to-connect-fed-management.md
https://stackoverflow.com/questions/50929537/aad-claims-upn-vs-on-premise-ad-upn