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I read a number of blog posts and found that it is tough to keep the secret-key a secret and if using a symmetric algorithm for JWT creation, the generator has the power to create as well as validate the JWT. This seems a place where it may be misused.

This brings in picture RSA-based (asymmetric algorithm for JWT creation). These JWT seem to be a better choice if we want single authority for JWT creation.

When should one use HMAC-based JWT?

It would be so nice if you could give an example scenario.

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You have a server which has a secret key. You want to give another party some type of claim (for example, you could give a user a token saying they're authenticated), so you sign it and hand the signed claim to that party. Then they can present that claim at a later time and you can verify:

  1. Authentication: that you signed it, assuming you didn't share your secret, and...

  2. Data Integrity: that the data has not been altered.

If you're sending a claim that another party needs to verify, then use an asymmetric digital signature algorithm, such as RSA. This is called Non-Repudiation and is not a property of HMACs.

Another example: You're sending another server some data that you expect that server to return to you at a later date, but you need to make sure that server didn't tamper with that data. You can sign it with an HMAC.

Ultimately this question is equivalent to: "What's the difference between MACs and DSAs?" and there is lots more reading under that topic.

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