Confidential and Public Applications
According to the OAuth 2.0 spec, applications can be classified as either confidential or public. The main difference relates to whether or not the application is able to hold credentials (such as a client ID and secret) securely. This affects the type of authentication the applications can use.
When you create an application using the Dashboard, Auth0 will ask you what Auth0 application type you want to assign to the new application and use that information to determine whether the application is confidential or public.
To learn more, read Check if Application is Confidential or Public.
Confidential applications
Confidential applications can hold credentials in a secure way without exposing them to unauthorized parties. They require a trusted backend server to store the secret(s).
Grant types
Because they use a trusted backend server, confidential applications can use grant types that require them to authenticate by specifying their client ID and client secret when calling the Token endpoint. They can use either the Post or the Basic Token endpoint authentication method.
These are considered confidential applications:
A web application with a secure backend that uses the Authorization Code Flow, Resource Owner Password Flow, or Resource Owner Password Flow with realm support
A machine-to-machine (M2M) application that uses the Client Credentials Flow
ID tokens
Because confidential applications are capable of holding secrets, you can have ID tokens issued to them that have signed in one of two ways:
Symmetrically, using their client secret (
HS256)Asymmetrically, using a private key (
RS256)
Public applications
Public applications cannot hold credentials securely.
Grant types
Public applications can only use grant types that do not require the use of their client secret. They can't send a client secret because they can't maintain the confidentiality of the credentials required.
These are public applications:
A native desktop or mobile application that uses the Authorization Code Flow with PKCE
A JavaScript-based client-side web application (such as a single-page app) that uses the Implicit Flow grant
ID tokens
Because public applications are unable to hold secrets, ID tokens issued to them must be:
Signed asymmetrically using a private key (
RS256)Verified using the public key corresponding to the private key used to sign the token