Dechea

If these three are your options, I would recommend going with Auth0. They have all functionality available as developer API (Okta e.g. not) so you can manage your instance with Infrastructure as code and can also easily add functionalities relatively easily with the API. They are also really powerful if we're talking about ABAC (Attribute based access control). You can also enrich your access token with custom claims from your MongoDB, that can be probably really useful, as you said that you're dealing with multi tenancy.

We're using Auth0 in combination with Fauna Fauna is a database, so it would challenge you're mongodb. But Faunadb is the first database that implemented a full end user ABAC system directly in the database. (And also a lot easier than the ABAC systems from Okta or Auth0). This helps us, to use Auth0 only as identity platform and doing all the authorization with enriched claims over Fauna. With that you can skip in a lot of the cases you're backend, and you can request directly from the frontend your database (Blazing fast). Also, you can replace in some years Auth0 a lot easier with some upcoming cheaper (Auth0 was bought by Okta for a hilarious price) and "easy to use" passwordless identity provider like Passage.id

Fauna is a serverless database where you store data as JSON. Also, you have build in a HTTP GraphQL interface with a full authentication & authorization layer. That means you can skip your Backend and call it directly from the Frontend. With the power, that you can write data transformation function within Fauna with her own language called FQL, we're getting a blazing fast application.

Also, Fauna takes care about scaling and backups (All data are sharded on three different locations on the globe). That means we can fully focus on writing business logic and don't have to worry anymore about infrastructure.