To check whether an access token belongs to a particular user in the resource server, you can use the OAuth2 token introspection endpoint. This is an API endpoint exposed by Ory that allows the resource server to verify the validity of the access token and other associated metadata. Here's an example of how to use the token introspection endpoint using the SDK:

javascript import { Configuration, OAuth2Api } from "@ory/client"      const ory = new OAuth2Api(    new Configuration({    basePath: `https://${process.env.ORY_PROJECT_SLUG}.<http://projects.oryapis.com|projects.oryapis.com>`,    accessToken: process.env.ORY_API_KEY,    }),   )      export async function introspectToken(accessToken: string) {    const { data } = await ory.introspectOAuth2Token({ token: accessToken })    data.active // true or false   }

In this example, the

introspectToken

function sends a request to the introspection endpoint with the access token as a parameter. The endpoint responds with information about the token, including its validity and other metadata. If the token is valid and active,

data.active

will be

true

. Remember, OAuth2 tokens are like money. They allow you to perform actions, but they don't necessarily prove the identity of the user. For authentication purposes, you should use OpenID Connect ID Tokens. Sources: - [OAuth2 token introspection](https://www.ory.sh/docs/hydra/guides/oauth2-token-introspection) - [Revoking JSON Web Tokens](https://www.ory.sh/docs/oauth2-oidc/jwt-access-token#revoking-json-web-tokens) - [Should I use OAuth2 tokens for authentication?](https://www.ory.sh/docs/hydra/faq#should-i-use-oauth2-tokens-for-authentication)