how do i login (impersonate) as another user in Jira?

[barbarat]

Trying to troubleshoot another user's possible permission issue (he is in all the same groups as myself and the rest of the team, but does not see the list of users to assign tickets to when entering part of the name). I'd like to login as the user to troubleshoot some more - this is for JIRA cloud.

[Dave]

It sounds like the user does not have the Browse Users global permission.  If you're an admin, type 'gg' to bring up the search box in JIRA and start typing Global Permissions - click on that result to check the groups assigned to the Browse Users global permission to ensure that user is a part of that - https://confluence.atlassian.com/display/JIRAKB/Unable+to+Browse+for+Users+and+Groups

[Scott Buchanan]

For future reference, this is now a feature in Cloud for users below site-admin level.

[Rene Dohmen]

I have the same problem; it would be very handy to impersonate another user to investigate complex workflow with permission problems (i'm Admin).

[Joel Chuah]

There isnt one for JIRA cloud AFAIK but its achievable on JIRA server installations with a plugin called Groovy Runner. This feature is accessible under the Built-In Script, Switch to a Different User.