Do you mean SSO for Office and JIRA or for Confluence and JIRA? If it's JIRA and Confluence within the same Cloud instance, that is already the behavior.
For other integrations, you can watch the following improvement request to be notified of the progress:
Jaime Kirch da Silveira
Atlassian Cloud Support
Sorry for being a little bit off-topic here as I guess you're looking for a solution for Atlassian Cloud only but I thought the following might be interesting for those of you who are trying to integrate their Office 365 identities with self hosted Atlassian products.
Thus you might want to take a look at the Office 365 Directory Connector for Crowd (ODCC) by Cleito: https://www.cleito.com/products/odcc/
The ODCC plugin allows you to manage your Atlassian users and groups in a central place which is Office 365 administration portal. With the ODCC plugin, an Office 365 account also becomes an Atlassian stack account and users enter their Office 365 credentials to log into Atlassian applications. Once logged into an application (e.g. Jira, Confluence) using Crowd as its user management system, users do not have to authenticate again thanks to Crowd SSO.
You can see it in action here: https://www.youtube.com/watch?v=SH8R_emN43U
(Disclaimer: I work for the vendor of this plugin)
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