Thank you for reaching us!
To answer your question, yes, it is possible. To achieve this, you can use Entra ID B2B collaboration to invite users from the Workforce tenant to the Customer tenant as guest users. Once the guest users are added to the Customer tenant, they can use their Workforce credentials to sign in to the customer-facing SPA.
For more information, please refer Workforce and external tenant configurations in Microsoft Entra External ID
Hope this helps. Do let us know if you any further queries.
Thanks,
Akhilesh.
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and Yes
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