Using JSON Web Tokens (JWTs) to secure your APIs has become an ad-hoc standard in the IT-industry. However, the underlying concepts and mechanisms can be complex and are often misunderstood.
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General advice when using JWTsUsing JWTs to handle sessions introduces new risks. Allways do a thorough risk assessment before you deploy to your production environment. Using JWTs assumes that all involved secrets are handled in a proper way in both API-clients and APIs. Secrets could be both passwords and cryptographic key material. Always make sure your secrets are kept safe! Do not accept unsafe JWTs with the JOSE header {"alg": none; }. JWTs should always be signed and should use a valid and correct signature scheme If a JWT contains sensitive data it should be encrypted
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Things to consider when using Access TokensA "self contained" JWT can not be revoked until it expires. Consider using referenced tokens if the token provides access to sensitive or high-risk data. Access Tokens should have a life-time that is as short as possible.
As a general principle: the more sensitive data an API exposes the shorter the life-time should be. To enhance the user experience sessions with a long life-span should be combined with Access Tokens that have short life-span. You can acheive this by using refresh tokens on the client.
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Always verify the integrity of the JWTAlways validate the token signature Make sure your libraries and frameworks always validates the token signature HelseID only offers signatures based on asymmetric algorithms
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DO NOT BLINDLY TRUST THE VALUE IN CLAIMSExamples: “kid” - do not perform certificate requests before the values are validated and verified “jku” or “x5u” are header values that point to a URL. Do NOT follow these URLs before they are validated in order to avoid SSRF attacks
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Always validate claims in the access tokenet
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Always verify the "exp" claim to make sure the token hasn’t expired
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Always verify the claim "nbf" to make sure the token actually is "active"
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Always verify the claim "iss" to make sure that the token issuer is someone you actually trust
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Always verify the claim "aud" to make sure that the token is intended for you
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Reject the request if the "aud" claim is missing
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If you use "scopes" for access control you must always make sure that the values in the “scope” claims are valid and correct.
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Always validate and verify that the value in the claim "security_level" corresponds with the requirements for your API.
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Always validate and verify the value in the claim "pid".
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Always validate and verify the value in the claim "hpr_nr".
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