Implement push notifications for signing requests

[Uxio0]

Push notifications registration changes

• Uuid field will be required (need to keep it optional for a while to support existing clients).
• Timestamp field: within the last 5 minutes from the current UTC time in epoch seconds format.
• Signatures field: array of signatures of the registration request by the owner keys imported in the client. Associate those signing addresses with the cloud messaging token. Hex string: 0x + hex(r) + hex(s) + hex(v + 27)

Add new type of notification CONFIRMATION_REQUEST

Sent on receiving new transaction for a Safe to those cloudMessaging tokens that have associated owner keys and those owner keys are owners of the safes that will have this transaction, and those keys did not sign that transaction.

Signature calculation

To calculate the signature, the following fields must be used:

• prefix: constant, it will be gnosis-safe
• timestamp:
• uuid: uuid of the device
• cloudMessagingToken
• safes: concat list of sorted checksummed addresses

So the hash must be calculated:
keccak256($prefix + timestamp + uuid + cloudMessagingToken + sorted(safes)

For example:

• prefix = “gnosis-safe”
• timestamp = 1605186645155
• uuid = “33971c4e-fb98-4e18-a08d-13c881ae292a”
• cloudMessagingToken = “dSh5Se1XgEiTiY-AXQAX21”
• safes = [“0xbDEbdd6CEE25b2F931D2FE265D70E1A533b02453”, “0xa2AC1760DAf52986421b1552bDCa04707e78950E”]

keccak256("gnosis-safe160518664515533971c4e-fb98-4e18-a08d-13c881ae292adSh5Se1XgEiTiY-AXQAX210xa2AC1760DAf52986421b1552bDCa04707e78950E0xbDEbdd6CEE25b2F931D2FE265D70E1A533b02453)

More details in the spec document https://docs.google.com/document/d/1RqIfZkqdS_TZ4IQVjeWUhNI1ZguD3NfpohSSRLVxB5Q/edit#