We are trying to implement SSO inside the MSTeams Tabs app. Our SSO URL redirects the user to the identity provider's URL for authentication.
We need to open the identity provider URL inside the teams tab as a pop-up.
We are not using the MsTeams suggested YoTeams scaffold, we are using MsTeams js library directly inside our react app, so we don't want to try the task tab.
You can't launch a popup directly for this - the Teams client will block you. However, the built-in SSO capability has a mechanism specifically to launch such a popup, and handle it's response. It sounds like you're using an external Identity Provider (i.e. not Azure AD), in which case there's some different work to usual, but it's documented. Please see https://learn.microsoft.com/en-us/microsoftteams/platform/tabs/how-to/authentication/tab-sso-overview and then https://learn.microsoft.com/en-us/microsoftteams/platform/tabs/how-to/authentication/auth-flow-tab