[AH] Ensure either the seller or the authority is passed as signer on the sell instruction

[lorisleiva]

• Creates a new SaleRequiresExactlyOneSigner error.
• Throw the new error when both the seller and the authority are passed as signers in the sell instruction.

See #911

[github-actions]

Workflow Verify package library found differences when running yarn api:gen in the JS lib for auction-house. Please see the job for more details: https://github.com/metaplex-foundation/metaplex-program-library/actions/runs/3676534980.

[austbot]

This change seems good, Is this motivated by web3 js throwing an error when a signer is not needed?

[lorisleiva]

Hey @austbot,

No because the program accepts the scenario where both the seller and the authority are passed as signers.

When that's the case, it just happens that:

• The fee_payer variable will be set to authority (See code).
• But the seller will still approve a new delegate authority on the token (See code).

The motivation behind this PR is that the invariant defined here don't match the code. Even though this ends up not causing a security threat, it's best to be explicit about what we expect to avoid bad surprises in the future.

This was raised by issue #911.

[stegaBOB]

Looks good to me. Easy approve on this one!

[samuelvanderwaal]

@lorisleiva this looks good to merge to me

[lorisleiva]

patch version

[jdnichollsc]

Hey folks, what do you think about this PR? <3 #1059