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

# SDK Authentication

The Classiq Python SDK authenticates your device with your Classiq account through an interactive, browser-based confirmation. For unattended, server-to-server contexts where no person can sign in, use the [Client Credentials (M2M) flow](/user-guide/authentication/m2m-authentication) instead.

## Authenticating your device

Make sure the SDK is installed before authenticating; see the [Python SDK installation guide](/getting-started/sdk_installation).

In Python, run:

[comment]: DO_NOT_TEST

```python theme={null}
import classiq
classiq.authenticate()
```

A confirmation window opens in your web browser. Confirm the authentication:

<Frame>
  <img src="https://docs.classiq.io/resources/signup_authentication.png" style={{width: "70%"}} />
</Frame>

Once confirmed, you are ready to use Classiq. The credentials are cached locally and refreshed automatically, so you only need to re-authenticate if they are missing, expired, or revoked.

## Re-authenticating

To replace cached credentials, for example after they expire or when switching accounts, overwrite them:

[comment]: DO_NOT_TEST

```python theme={null}
import classiq
classiq.authenticate(overwrite=True)
```

## Troubleshooting

<Accordion title="Device is not authenticated">
  Overwrite the cached credentials and authenticate again, as described in [Re-authenticating](#re-authenticating).
</Accordion>

<Accordion title="Auth0 error code 403: access denied">
  This error means your authentication credentials were denied. Overwrite them as described in [Re-authenticating](#re-authenticating).
</Accordion>

<Accordion title="Authentication on headless Linux systems">
  The authentication procedure on headless Linux systems stores the tokens locally in a credentials file. You must still run the authentication once, but it can be done on another system that has a browser, then the credentials file copied over.
</Accordion>

<Accordion title="Confidential information pop-up on Apple computers">
  On some Apple computers, a system pop-up may appear during authentication:

  <Frame>
    <img src="https://docs.classiq.io/resources/signup_access_mac.png" style={{width: "70%"}} />
  </Frame>

  Type your device password and click **Always Allow** twice.
</Accordion>

If the problem persists, ask in the [community Slack](https://short.classiq.io/join-slack).