Register recovery agent from the signup service

[gryaele]

This pull request extends the ManageRecoveryBindingRequest struct and updates related logic and tests to support recovery agent updates in the recovery bindings flow. The main changes add new fields for signature, nonce, and the new recovery agent address, and ensure these are handled throughout the codebase and tests.

Recovery agent update support

• Added signature, nonce, and new_recovery_agent fields to the ManageRecoveryBindingRequest struct in pop_backend_client.rs to support recovery agent update operations. ([walletkit-core/src/issuers/pop_backend_client.rsR16-R22](https://github.com/worldcoin/walletkit/pull/349/files#diff-3824125edaf8fa9a81da332d83ba961405575a0321b8f820a336f9ec4c62eb00R16-R22))
• Updated the bind_recovery_agent and unbind_recovery_agent methods in recovery_bindings_manager.rs to generate and include the new fields when constructing ManageRecoveryBindingRequest, using the authenticator to sign the update and pass the new recovery agent address. ([[1]](https://github.com/worldcoin/walletkit/pull/349/files#diff-592fea17b31859cf09d8c8fe2190249b35dd84316d9d99180a0d6ff2b3fbd23fR81-R93), [[2]](https://github.com/worldcoin/walletkit/pull/349/files#diff-592fea17b31859cf09d8c8fe2190249b35dd84316d9d99180a0d6ff2b3fbd23fL112-R134))

Test updates

• Modified all related tests in both pop_backend_client.rs and recovery_bindings_manager.rs to include and validate the new fields (signature, nonce, new_recovery_agent) in requests and mock expectations. ([[1]](https://github.com/worldcoin/walletkit/pull/349/files#diff-3824125edaf8fa9a81da332d83ba961405575a0321b8f820a336f9ec4c62eb00R226-R242), [[2]](https://github.com/worldcoin/walletkit/pull/349/files#diff-3824125edaf8fa9a81da332d83ba961405575a0321b8f820a336f9ec4c62eb00R271-R287), [[3]](https://github.com/worldcoin/walletkit/pull/349/files#diff-3824125edaf8fa9a81da332d83ba961405575a0321b8f820a336f9ec4c62eb00R324-R337), [[4]](https://github.com/worldcoin/walletkit/pull/349/files#diff-3824125edaf8fa9a81da332d83ba961405575a0321b8f820a336f9ec4c62eb00R366-R383), [[5]](https://github.com/worldcoin/walletkit/pull/349/files#diff-592fea17b31859cf09d8c8fe2190249b35dd84316d9d99180a0d6ff2b3fbd23fR249-R250), [[6]](https://github.com/worldcoin/walletkit/pull/349/files#diff-592fea17b31859cf09d8c8fe2190249b35dd84316d9d99180a0d6ff2b3fbd23fL235-R263), [[7]](https://github.com/worldcoin/walletkit/pull/349/files#diff-592fea17b31859cf09d8c8fe2190249b35dd84316d9d99180a0d6ff2b3fbd23fL257-R288), [[8]](https://github.com/worldcoin/walletkit/pull/349/files#diff-592fea17b31859cf09d8c8fe2190249b35dd84316d9d99180a0d6ff2b3fbd23fL288-R328), [[9]](https://github.com/worldcoin/walletkit/pull/349/files#diff-592fea17b31859cf09d8c8fe2190249b35dd84316d9d99180a0d6ff2b3fbd23fR394-R395))

Code quality and consistency

• Defined a ZERO_ADDRESS constant for use as the null recovery agent address, improving readability and consistency. ([walletkit-core/src/issuers/recovery_bindings_manager.rsL21-R22](https://github.com/worldcoin/walletkit/pull/349/files#diff-592fea17b31859cf09d8c8fe2190249b35dd84316d9d99180a0d6ff2b3fbd23fL21-R22))
• Updated documentation for bind_recovery_agent to include the new parameter. ([walletkit-core/src/issuers/recovery_bindings_manager.rsR70](https://github.com/worldcoin/walletkit/pull/349/files#diff-592fea17b31859cf09d8c8fe2190249b35dd84316d9d99180a0d6ff2b3fbd23fR70))

[gryaele]

Leaf index can be take from the authenticator, but I also noticed that it's sometimes passed as a param. What is the recommendation here?

[Dzejkop]

imo we should take it from the authenticator. Can we also take sub?

[gryaele]

we'd need blinding factor I think, I couldn't find a method to get the sub in the Authenticator