An identity provider authenticates users and tells your applications who they are. Once several applications depend on it, replacing it means reconfiguring every one, migrating credentials that in many cases cannot be exported, and asking users to re-enrol their second factors. Choose accordingly.
The realistic options divide into three groups. Bundled providers such as Microsoft Entra ID come with a productivity suite you may already pay for, and are hard to beat on cost if your organisation is already there. Independent providers such as Okta or Auth0 tend to be stronger on developer-facing features and multi-tenant scenarios. Self-hosted options such as Keycloak remove the licence cost and replace it with an operational burden that is real.
Separate the two populations before deciding. Employee identity and customer identity have different requirements — employees need lifecycle management, joiners and leavers, group-based access; customers need registration flows, social login, and scale. A tool excellent at one is often mediocre at the other, and using one product for both usually compromises the customer experience.
Check the standards support carefully. SAML and OIDC are table stakes. SCIM for user provisioning is what enterprise buyers ask for and what saves you from manual account creation. If you sell to enterprises, their security questionnaire will ask about all three.
Price on the growth curve, not today. Per-active-user pricing that is comfortable at a thousand users can be uncomfortable at fifty thousand, and features like advanced multi-factor or fine-grained authorisation often sit in a higher tier than the one you are quoted.
Whatever you choose, keep an emergency access account that does not depend on the provider being available. An identity provider outage with no break-glass path locks you out of your own infrastructure at precisely the wrong moment.
