Bitbucket Pull Request from Command Line using SSH Access Keys
I guess it is about a Bitbucket Server instance here, right?
According this documentation there is just Basic Authentication, OAuth or Session Authentication. https://developer.atlassian.com/server/bitbucket/how-tos/command-line-rest/#authentication
One addition to Basic Authentication are the Personal Access Tokens, which can be generated per user and can be used as a password too: https://confluence.atlassian.com/bitbucketserver0516/personal-access-tokens-966061199.html#Personalaccesstokens-usingpersonalaccesstokens
But, I guess for you the most proper solution would be to create an Application Link and use OAuth.