OAuth 2.0 device flow lets an input-limited device—such as a TV or printer—start an authorization request while you sign in and approve it on a phone or computer. The original device then polls the authorization server for the result; your phone does not send the token to the TV. The flow is useful when the device has no suitable browser or practical way to enter credentials, but you should verify that the request is for the device in front of you before approving it.
How does OAuth device flow work?
Defined in RFC 8628, the OAuth 2.0 Device Authorization Grant is a handoff between an internet-connected client with limited input or no suitable browser and a second device that can handle a browser-based sign-in. Smart TVs, media consoles, picture frames, and printers are examples in the specification. The constrained device needs outbound HTTPS and a way to show you a URI and code; you use a phone or computer to complete authorization.
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The flow is not a general replacement for browser-based OAuth. If an app can provide a suitable browser-based sign-in on the same device, RFC 8628 says device authorization is not intended to displace it.
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1. The device requests authorization
When you choose to sign in or connect an account, the client sends a device authorization request to the authorization server, identifying itself and, where relevant, the requested scope. The specification says a client should not start this automatically at launch or repeatedly after a failed attempt: polling without a user-ready authorization session creates unnecessary server load.
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2. The server returns two different codes
The server responds with a high-entropy device_code for the client’s later token request, plus a shorter user_code for you to enter. It also supplies a verification_uri, an expiration time, and a polling interval. These codes have different jobs: the device code is for the client’s back-channel request and is not meant to be shown to you; the user code links your browser session to the pending authorization.
3. You open the verification page
The device displays instructions to visit the verification URI on another device and enter the user code. Some authorization servers provide verification_uri_complete, which can streamline the handoff, for example with a QR code. A shortcut changes how you reach the page, not what you are approving: check the device information and authorization request before continuing.
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4. You authenticate and approve or deny
The authorization server validates the user code, authenticates you, and presents the request for approval or denial. The exact browser screens depend on the server. Signing in successfully is not the same as confirming that the pending request came from your own TV, console, or other device.
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While you complete the browser step, the original client repeatedly sends a token request using its device code and the device-code grant type. Once authorization succeeds, the token endpoint returns the token response to that client. This polling design means your phone does not need to transmit a token directly to the TV.
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6. The client follows the server’s response
Polling is governed by the protocol’s interval and response codes. A client must not poll faster than allowed, and it must stop when the authorization cannot continue.
| Response | What the client does |
|---|---|
authorization_pending |
Wait the required interval, then continue polling. |
slow_down |
Add five seconds to the polling interval for this and subsequent requests. |
access_denied |
Stop polling; authorization was denied. |
expired_token |
Stop polling; the device authorization session has expired. |
| Connection timeout | Reduce polling frequency; RFC 8628 recommends exponential backoff. |
| Other error | Stop polling. |
Why is my TV asking me to enter a code on another device?
The TV likely cannot offer a practical browser sign-in or convenient text entry. Instead, it starts the request and shows a short-lived code; a phone or computer handles the authentication page and approval. The TV learns the result by polling the authorization server. The prompt is therefore a sign-in handoff, not a request for your phone to send your password or token to the TV.
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Only continue if you deliberately started the sign-in on that TV and the authorization page identifies the device or service you expect. A real login page can still be used to approve someone else’s pending request.
How to tell a legitimate prompt from a device-code phishing attempt
In a device-code phishing attack, someone else initiates a device flow and persuades you to enter their code on the genuine verification site. You may authenticate with the real identity provider and still authorize the wrong device. The site’s legitimacy alone does not establish who initiated the request.
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- Start with a sign-in action you initiated on the device in your possession. Be wary of an unexpected request to enter a code, especially one arriving through a message, call, or unrelated webpage.
- Read the authorization page’s device, app, or service details. Stop if they do not match the device and account action you intended.
- Do not treat a QR code or complete-URI link as proof of legitimacy. It can simplify code entry, but you still need to confirm what is being authorized.
- Do not share a displayed user code with someone who asks you to enter it on their behalf. The code connects an authorization request to your browser session.
RFC 8628 recommends telling users that they are authorizing a device and confirming that it is in their possession. It also highlights safeguards such as rate-limiting user-code attempts, using a high-entropy device code, keeping user-code lifetimes usable but short enough to limit reuse for phishing, and considering who can see codes displayed on a device.
Security guidance for teams implementing cross-device authorization
RFC 10027, an IETF Best Current Practice published in August 2026, covers security for cross-device flows, including RFC 8628. It calls for a risk assessment before implementation, suitable mitigations for identified risks, and avoiding cross-device flows when risks cannot be sufficiently mitigated. It also recommends including proximity as a mitigation when possible. This is newer security guidance for evaluating the design; it does not replace the device authorization protocol.
For token protection more broadly, RFC 9700, the OAuth 2.0 Security Best Current Practice published in January 2025, recommends sender-constraining access tokens, for example with mutual TLS or DPoP, to reduce the risk of misuse if tokens are stolen or leaked. That advice applies to OAuth security generally, not only to device flow.
Microsoft Entra’s device-code implementation
Microsoft documents device authorization in Microsoft Entra for input-constrained devices. Its example uses a /devicecode request followed by polling the /token endpoint. The guide gives a default expires_in period of 15 minutes for that implementation; it is not a universal RFC 8628 lifetime. Microsoft recommends using its supported Microsoft Authentication Libraries (MSAL) where possible.
Microsoft’s security operations guidance says successful device-code-flow sign-ins in an environment with no corresponding need should be investigated. Entra sign-in logs are a monitoring source, and Conditional Access can be configured to block or allow device-code flow. Available policies and interfaces depend on the tenant and can change.
Quick Recap
When device flow is the right choice
| Decision | When it fits | What to weigh |
|---|---|---|
| Device flow or same-device browser authorization | Use device flow when the client lacks a suitable browser or practical input. | For a capable native app, RFC 8628 does not position device flow as a replacement for browser-based OAuth. |
| Manual code or complete URI/QR handoff | A complete URI or QR can reduce typing and navigation. | The user still needs to verify which device and request they are authorizing. |
| Convenience or cross-device risk | Use the handoff when moving authentication to a capable device provides a real usability benefit. | Assess cross-device phishing and session-transfer threats, then select mitigations appropriate to the deployment. |
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