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61 lines
2.6 KiB
Markdown
61 lines
2.6 KiB
Markdown
# API Authentication
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!!! info "Design Document"
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This is a design document, explaining the design and vision for a HedgeDoc 2
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feature. It is not a user guide and may or may not be fully implemented.
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## Public API
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All requests to the public API require authentication using a [bearer token][bearer-token].
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This token can be generated using the profile page in the frontend
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(which in turn uses the private API to generate the token).
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### Token generation
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When a new token is requested via the private API, the backend generates a 64 bytes-long secret of
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cryptographically secure data and returns it as a base64url-encoded string,
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along with an identifier. That string can then be used by clients as a bearer token.
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A SHA-512 hash of the secret is stored in the database. To validate tokens, the backend computes
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the hash of the providedsecret and checks it against the stored hash for the provided identifier.
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#### Choosing a hash function
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Unfortunately, there does not seem to be any explicit documentation about our exact use-case.
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Most docs describe classic password-saving scenarios and recommend bcrypt, scrypt or argon2.
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These hashing functions are slow to stop brute-force or dictionary attacks, which would expose
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the original, user-provided password, that may have been reused across multiple services.
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We have a very different scenario:
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Our API tokens are 64 bytes of cryptographically strong pseudorandom data.
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Brute-force or dictionary attacks are therefore virtually impossible, and tokens are not
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reused across multiple services.
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We therefore need to only guard against one scenario:
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An attacker gains read-only access to the database. Saving only hashes in the database prevents the
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attacker from authenticating themselves as a user. The hash-function does not need to be very slow,
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as the randomness of the original token prevents inverting the hash. The function actually needs to
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be reasonably fast, as the hash must be computed on every request to the public API.
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SHA-512 (or alternatively SHA3) fits this use-case.
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## Private API
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The private API uses a session cookie to authenticate the user.
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Sessions are handled using [passport.js](https://www.passportjs.org/).
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The backend hands out a new session token after the user has successfully authenticated
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using one of the supported authentication methods:
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- Username & Password (`local`)
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- LDAP
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- SAML
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- OAuth2
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- GitLab
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- GitHub
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- Google
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The `SessionGuard`, which is added to each (appropriate) controller method of the private API,
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checks if the provided session is still valid and provides the controller method
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with the correct user.
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[bearer-token]: https://datatracker.ietf.org/doc/html/rfc6750
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