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Vivek_Yadav's avatar
Vivek_Yadav
New member | Level 1
25 days ago

Dropbox OAuth2 Issue: Scope Parameter Handling

According to OAuth2 Authorization documentation, the scope parameter is nullable, and as per RFC 6749, parameters without a value must be treated as omitted, with unrecognized parameters ignored.

 

However, Dropbox's OAuth2 implementation returns the following error when the scope parameter is included:

 

Error:

 "error": "invalid_request", 

 "error_description": "unknown field \"scope\""

 

This behavior violates OAuth2 standards, as unrecognized parameters should not cause a failure.

    • DB-Des's avatar
      DB-Des
      Icon for Dropbox Engineer rankDropbox Engineer

      Vivek_Yadav,

      Thank you for following up. At this time, we don’t have any updates to share. Please rest assured that we’ll reach out to you as soon as we have any developments to report. 

  • DB-Des's avatar
    DB-Des
    Icon for Dropbox Engineer rankDropbox Engineer

    Hi Vivek_Yadav,

    Including the scope parameter without value in the Auth URL does omit it and allows authorization to continue.

    For example, the following two Auth URLs work without issues:

    • https://www.dropbox.com/oauth2/authorize?client_id=<APP_KEY>&response_type=code&scope
    • https://www.dropbox.com/oauth2/authorize?client_id=>APP_KEY>&response_type=code&scope=

     

    In order to further investigate the error you have reported, please reply with:

    • the steps to reproduce the issue, including relevant code snippet(s), but don't include any access or refresh token(s)
    • the full text of any error or unexpected output
      • DB-Des's avatar
        DB-Des
        Icon for Dropbox Engineer rankDropbox Engineer

        Hi Vivek_Yadav 

        The oauth2/token endpoint allows the scope parameter only with a refresh_token because it aligns with OAuth 2.0 standards and best practices.

        When using a refresh token, the scope parameter lets you request a subset of the originally granted permissions, ensuring least-privilege access and better security. For other grant types (such as authorization_code in your example), the scope is determined during the initial authorization process, based on user consent. Allowing the scope parameter in these cases could bypass this consent, potentially introducing security risks.

        Further, RFC 6749 § 4.1.3, does not require the scope parameter, nor does it list it as optional, when using authorization_code as the grant type.

        This restriction ensures compliance with the OAuth specification and helps maintain secure, user-approved access to resources.

        Let us know if you have further concerns.