The best alternatives to Aserto are Authorizer, Oso Cloud, and PayRequest. If these 3 options don't work for you, we've listed a few more alternatives below.
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Authorizer is an open-source authentication and authorization solution for your applications. Bring your database and have complete control over the user information. You can self-host authorizer instances and connect to any SQL database.
Oso is a batteries-included system for authorization. Drop Oso Cloud into your apps to quickly add roles, sharing, fine-grained access, or any other access model you can think of.
Warrant helps developers add authorization and access control to their apps. Easily define access control rules and check against them in your app at runtime via API. Warrant manages all the complexity so you can focus on building your core product.