Scopes in API refer to the level of access that an application has to the data and functionality of an API (Application Programming Interface). At a high level, scopes allow the API provider to grant limited and specific permissions to client applications consuming the API.
When a client application wants to use an API, it needs to request access from the API provider. The provider can then grant permission to the client by issuing “scopes”, which are like access keys that specify what data and functions the app is allowed to use. Scopes allow the provider to restrict and control what a client can do, rather than just giving full unrestricted access.
Why are scopes important in APIs?
Scopes play a critical role in allowing APIs to securely provide access to applications. Here are some of the main reasons scopes are important:
- Security – Scopes allow the API provider to grant limited access. This prevents applications from accessing data or performing actions they should not be allowed to do.
- Privacy – Scopes enable personal or sensitive data to be protected. The provider can restrict which scopes can read/write private user information.
- Access control – Different applications may get access to different scopes depending on their needs. Some apps may only need read-only permission while others need broader access.
- Granularity – Scopes allow access to be defined down to very specific levels, e.g. permission to only update one field in a database.
- API evolution – New scopes can be added over time as the API expands without breaking existing client integrations.
Overall, scopes allow providers to open up APIs to third-party applications in a controlled way without compromising security or functionality.
How do scopes work in an API call?
Here is a high-level overview of how scopes work when an application makes an API request:
- Client app registers with the API provider and requests access to specific scopes.
- If approved, the provider grants a token containing the allowed scopes.
- The client passes the token in the API request headers.
- The API verifies the token and checks the scopes.
- If the scopes permit the requested action, the API processes the request.
- If not, the API rejects the request and returns an error.
In this flow, the scopes provided by the API provider act like permissions determining what the client is authorized to do. The client remains in control of which data it actually requests, but scopes define the boundaries of access.
How are scopes defined in an API?
Scopes are defined by the API provider when configuring endpoint permissions in the API. Here are some ways scopes are commonly implemented:
- String values – Scopes are defined as string literals like “read”, “write”, “update:profile”.
- Structured values – Scopes can have a structured syntax like “resource:action” e.g. “users:create”.
- Enumerated values – Scopes are defined as constants or enumerations in code like SCOPE_READ, SCOPE_WRITE.
- Bitmasks – A bitmask can encode multiple scopes in a single integer value.
- Objects/classes – Object-oriented languages can define scopes using classes with granted permissions.
The scoping model needs to be documented so client developers understand what access each scope grants. Some APIs also provide a discovery process for looking up available scopes.
Examples of scopes in popular APIs
To understand how scopes are used in the real-world, here are some examples from popular APIs:
Google OAuth Scopes
- https://www.googleapis.com/auth/calendar.readonly – Grants read access to a Google Calendar.
- https://www.googleapis.com/auth/drive.file – Permits access to files on Google Drive.
- https://www.googleapis.com/auth/youtube – Enables full access to YouTube data.
Google uses string values for scopes and groups them into APIs like Calendar or Drive. Apps request the specific scopes they need.
Facebook API Scopes
- public_profile – Access to basic profile information.
- instagram_basic – Ability to read an Instagram user’s profile.
- read_insights – View Facebook analytics and insights.
Facebook also uses string values for scopes. Apps can request multiple scopes separated by commas in the API call.
Azure AD Scopes
- User.Read – Read-only access to user profile data.
- Directory.Read.All – Read directory data like users and groups.
- Domain.ReadWrite.All – Manage domains.
Azure Active Directory leverages a structured scope syntax of “resource.operation”. This allows more precise control over the permissions granted.
Best practices for implementing and using scopes
Here are some best practices around working with scopes in APIs:
- Document scopes clearly – Be transparent about what access each scope allows.
- Use appropriate naming – Name scopes for clarity using domain terminology.
- Limit broad scopes – Try not to define scopes that are overly broad or powerful.
- Follow principle of least privilege – Apps should request the minimum scopes needed.
- Validate scopes strictly – Verify scopes on the server before granting access.
- Monitor for anomalies – Watch for apps using scopes they shouldn’t need and investigate.
- Rotate tokens periodically – Re-check scopes rather than granting endless access.
- Support incremental auth – Allow apps to request additional scopes later if needed.
- Provide discovery – Have a way for consumers to enumerate available scopes.
Common challenges with scopes
Here are some common challenges and issues that arise around scopes:
- Too many scopes – Having hundreds of scopes can overwhelm consumers and be hard to manage.
- Scope explosion – Adding new scopes frequently can increase complexity exponentially.
- Obsolete scopes – Old unused scopes should be removed to reduce clutter.
- Scope overlap – Similarly named or purposed scopes create confusion.
- User confusion – End users may not understand what scopes mean when authorizing apps.
- Hardcoded scopes – Client apps may request more scopes than they actually need.
- Scope changes – Modifying or removing scopes can break existing integrations.
API providers should aim for a scoped model that is intuitive, minimal, and evolves cautiously over time. Consumers should be thoughtful regarding which scopes their apps request.
Conclusion
Scopes play a critical role in controlling access and enabling secure integrations between APIs and client applications. They allow providers to open up APIs to external usage without compromising security or functionality. Implementing scopes requires striking a balance between granular control and complexity. On the consumer side, scopes should be requested judiciously based on the principle of least privilege. Overall, used properly, scopes are a powerful mechanism for building safe, scalable, and extensible API ecosystems.