> ## Documentation Index
> Fetch the complete documentation index at: https://docs.abbyy.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Authentication

> Authenticate requests to the ABBYY Vantage API: choose an OAuth 2.0 flow (Authorization Code, Client Credentials, or Password) and pass the access token.

Each HTTP request to the service should include an authorization header that ABBYY Vantage will use to confirm your identity. Contact ABBYY to request a tenant in ABBYY Vantage service. Once you have a tenant's account, you can create user accounts. The user account's email and password can be used to get an access token for API authorization.

The OAuth 2.0 protocol is used in ABBYY Vantage for authentication. OAuth 2.0 authentication is carried out over two stages: getting an access token and then the authorization itself.

Access tokens can be obtained using three standard authentication schemes: Resource Owner Password Credentials, Authorization Code Flow, and Client Credentials Flow.

## OpenID Connect Discovery Document

You can set up your application using OpenID Connect (OIDC) Discovery Document. For information about obtaining a tenant identifier, see the **Getting a Tenant Identifier** section of the Administrator's guide.

**Sample request:**

<CodeGroup>
  ```text US theme={null}
  https://vantage-us.abbyy.com/auth2/TestTenant/.well-known/openid-configuration
  ```

  ```text EU theme={null}
  https://vantage-eu.abbyy.com/auth2/TestTenant/.well-known/openid-configuration
  ```

  ```text AU theme={null}
  https://vantage-au.abbyy.com/auth2/TestTenant/.well-known/openid-configuration
  ```
</CodeGroup>

We also recommend using URLs found in the discovery document for ROPC and Authorization Code flows.

## Authentication Flow

<Steps>
  <Step title="Get an Access Token">
    Choose one of the three authentication methods to obtain an access token:

    * **Resource Owner Password Credentials (ROPC)** - Direct username/password authentication
    * **Authorization Code Flow** - OAuth redirect-based authentication
    * **Client Credentials Flow** - Machine-to-machine authentication with a client ID and secret
  </Step>

  <Step title="Include Token in Requests">
    Add the access token to the authorization header of all API requests.
  </Step>
</Steps>

## Next Steps

* [Resource Owner Password Credentials (ROPC)](/vantage/developer/authentication/resource-owner-password-credentials) - Recommended for server-to-server applications acting as a user
* [Authorization Code Flow](/vantage/developer/authentication/authorization-code-flow) - Recommended for user-facing applications
* [Client Credentials Flow](/vantage/developer/authentication/client-credentials) - Recommended for machine-to-machine integrations