The open source ory ecosystem ( http://github.com/ory/ ) might have what you're looking for, but it's definitely for advanced usecases. I know a lot of people that worked with Auth0/Okta/AWS Cognito but got so frustrated by downtimes, bugs, and complexity that they moved away. But it is an option for rapid prototyping although I'd keep a "replace it" somewhere in my milestone planning. Another possibility is Keycloak which is very enterprise / java fullstack and quite complex to understand.

Most advice in the comments is pretty bad though. Stuff like "API Clients need bearer tokens" is completely backwards and pushed by marketing people from companies (Auth0, Okta, ...) that misuse open protocols (OAuth2, OIDC) as a way to legitimize the closed source saas approach they took. Along the lines "if it looks complex it looks secure because most people have no idea". It's actually very easy to use cookies (httpOnly, secure) with API clients and you're saving yourself so much complexity with refreshing tokens and all that stuff.

Yet another possibility for super rapid prototyping is: https://github.com/bitly/oauth2_proxy

edit:// I forgot KeyCloak, but it's also for advanced enterprise use cases (SAML, OIDC, Realms, ...) and (from what I've heard) with a steep learning curve and heavy.