Hi,
since a couple of days, when we access the collections of an external team a guests, postman automatically redirect us to auth.atlassian.com without any reason. We talked with the Team and they didn’t activated anything regarding atlassian / jira.
Anyone have an idea of what is happening?
Sounds like they have setup SSO for that workspace using Atlassian as the OAuth providor.
Jira may auto-authenticate if you’re already logged in via SSO or have an active session cookie. Try clearing cookies or logging out from all sessions to stop it.
We don’t have Jira therefore we never logged in via their SSO 
They said that they didn’t changed anything, but will ask again with what you suggest maybe it will ring them some bells.
I’ve often heard “we haven’t changed anything,” and then it turns out something has changed. So it’s always worth double-checking!
Just a quick check — can you confirm that you’re able to access your own team’s workspaces?
I asked them, still waiting for an answer.
I have access to my team and all my workspaces and they do not redirect me like that. All workspaces in the guest team is doing the redirection.
It also looks like other people are reporting OAuth authentication issues (since last Friday) which might relate to this.
Seems like the others issues regarding the OAuth authentication got resolved but the redirection to Jira is still present. 
My guess, is that it is related to Guest account, because the users that have a proper role in the team doesn’t get that type of redirection.
I had the same issue and fixed it by deleting all cookies related to the site from Postman’s cookie manager. After that, the weird auto-auth stopped happening.
Turns out it was enforcing new auth redirects even for external users. Switching over to use https://acupowererp.com/products/jira-and-acumatica-cloud-erp for some of our workflows helped bypass manual login issues and kept billing and time tracking in sync.
