The access token and ID token are issued by Ory Hydra after the user has been successfully authenticated and has given consent. This process involves several steps and multiple endpoints, including the login endpoint and the consent endpoint. Here's a brief overview of the process: 1. The user agent (browser, mobile device) is redirected to the login endpoint (e.g., `todo24.com/login`) where the user is authenticated. 2. Upon successful authentication, the login endpoint redirects the user back to Ory Hydra. 3. Ory Hydra then needs the user's consent. It redirects the user agent to the consent endpoint (e.g., `todo24.com/consent`) where the user is asked to grant certain permissions. 4. Once the user gives consent, the consent endpoint redirects back to Ory Hydra. 5. Ory Hydra validates the request and issues the access, refresh, and ID tokens. You can validate the access tokens which are sent to your API directly at Ory Hydra, or use an Identity & Access Proxy like Ory Oathkeeper to do it for you. For more details, please refer to the [Ory Hydra case study](https://www.ory.sh/docs/hydra/case-study) in the documentation.

The client ID and client secret are used to authenticate a client application during the OAuth2 flow. They are passed in different ways depending on the authentication mechanism being used: 1. Basic Authentication: The client ID and client secret are sent as part of the Authorization header in an HTTP request. The Authorization header contains a Base64-encoded string of

{URL-encoded-client-ID}:{URL-encoded-client-secret}

. Here's an example of how to use Basic Authentication to obtain an access token:

javascript const clientID = "the-client-id"   const clientSecret = "the-secret-id"   const basicAuth = bas64_encode(url_encode(clientID) + ":" + url_encode(clientSecret))      const requestOptions = {    method: "POST",    headers: {    Authorization: "Basic " + basicAuth,    "Content-Type": "application/x-www-form-urlencoded",    },    body: "grant_type=client_credentials&scope=read",   }      fetch("<https://your-project.projects.oryapis.com/oauth2/token>", requestOptions)    .then((response) => response.json())    .then((data) => console.log(data))

(Source: [Basic Authentication](https://www.ory.sh/docs/oauth2-oidc/client-credentials#basic-authentication)) 2. Body Authentication: The client ID and client secret are sent as parameters in the body of the HTTP request. Here's an example of how to use Body Authentication to obtain an access token:

javascript const clientID = "the-client-id"   const clientSecret = "the-secret-id"      const qs = new URLSearchParams()   qs.set("grant_type", "client_credentials")   qs.set("client_id", clientID)   qs.set("client_secret", clientSecret)   qs.set("scope", read)      const requestOptions = {    method: "POST",    headers: { "Content-Type": "application/x-www-form-urlencoded" },    body: qs.toString(),   }      fetch("<https://your-project.projects.oryapis.com/oauth2/token>", requestOptions)    .then((response) => response.json())    .then((data) => console.log(data))

(Source: [Body Authentication](https://www.ory.sh/docs/oauth2-oidc/client-credentials#body-authentication)) 3. JWT Bearer Grant Type: Instead of sending the client ID and client secret, the client sends a JSON Web Token (JWT) which was signed by its cryptographic key. The client is created with the following command:

bash ory create oauth2-client --project "$project_id" \    --name "Client Credentials Demo" \    --grant-type client_credentials \    --token-endpoint-auth-method private_key_jwt \    --jwks-uri <https://example.org/path/to/clients/public_key_set.jwks>

(Source: [JWT Bearer profile for OAuth2 client authentication Part 1](https://www.ory.sh/docs/oauth2-oidc/client-credentials#jwt-bearer-profile-for-oauth2-client-authentication)) Remember, the client ID and client secret should be kept confidential and not exposed to the public.