Auth0, the billion-dollar Seattle-area startup that is a leader in identity authentication software, is being acquired by Okta, another leader in the space, the companies announced Wednesday. The all-stock deal is valued at approximately $6.5 billion — one of the largest acquisitions of a Seattle tech company. Auth0 was co-founded in 2013 by Eugenio Pace, who formerly ran the patterns and practices group at Microsoft, and Matias Woloski, a software engineer who remains the company’s CTO.