head to head · open source
hydra vs cas
hydra has 17,646 GitHub stars, 1,619 forks, 98 open issues and last shipped 3 months ago. cas has 11,394 stars, 3,955 forks, 17 open issues and last shipped yesterday. hydra leads on adoption by 55% (17,646 vs 11,394 stars). hydra is written in Go under Apache-2.0; cas is written in Java under Apache-2.0. hydra has attracted 9% as many forks as stars, cas 35%. cas was the more recently maintained of the two, and both are self-hostable with no licence fee. The two share 2 topic tags (authorization, oauth2), so they are genuine substitutes rather than adjacent tools.
Two open source projects, one decision. Both are free and self-hostable — the differences are community size, license terms, language stack and release pace.
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Side by side
| hydra | cas | |
|---|---|---|
| GitHub stars | ★ 18K | ★ 11K |
| License | Apache-2.0 | Apache-2.0 |
| Written in | Go | Java |
| Last push | 2026-07-29 | 2026-11-04 |
| Forks | ⑂ 1.6K | ⑂ 4.0K |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick hydra if
- You weight community size — 18K stars and counting
- You want the Apache-2.0 license terms
- Your stack matches Go
- You value the larger contributor base for long-term maintenance
pick cas if
- You want the cas feature set and don't need the biggest community
- You prefer the Apache-2.0 license terms
- Your stack matches Java
- You evaluated both and cas fits your workflow better
About hydra
Chat · Discussions · Newsletter · Docs · Try Ory Network · Jobs Ory Hydra is a hardened, OpenID Certified OAuth 2.0 Server and OpenID Connect Provider optimized for low latency, high throughput, and low resource consumption. It connects to your existing identity provider through a login and consent app, giving you absolute control over the user interface and experience. What is Ory Hydra? Why Ory Hydra OAuth2 and OpenID Connect: Open Standards OpenID Connect Certified Deployment options Use Ory Hydra on the Ory Network Self host Ory Hydra Quickstart Who is using Ory Hydra Ecosystem Ory Kratos: Identity and User…
read the full hydra overview →
About cas
Central Authentication Service (CAS) [ ][casslack] [ ][cassupport] Introduction Welcome to the home of the [Central Authentication Service project][apereocas], more commonly referred to as CAS. CAS is an enterprise multilingual identity provider and single sign on solution for the web and attempts to be a comprehensive platform for your authentication and authorization needs. CAS is an open and well documented authentication protocol. The primary implementation of the protocol is an open source Java server component by the same name hosted here, with support for a plethora of additional authentication protocols…
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Frequently asked questions
Is hydra or cas more popular?
hydra has 17,646 GitHub stars and cas has 11,394. hydra has the larger community by that measure.
Are hydra and cas free?
Both are open source. hydra is licensed under Apache-2.0 and cas under Apache-2.0. Neither carries a licence fee.
What is the difference between hydra and cas?
hydra is written in Go and cas in Java. The practical differences are community size, licence terms, language stack and release cadence — all compared in the table above.
Which should I choose, hydra or cas?
Choose hydra if you want the larger community (17,646 stars) or its Apache-2.0 licence terms. Choose cas if its feature set, stack or Apache-2.0 licence fits better. Both are self-hostable.