I know that clique.propose can be manually entered into geth and then all other nodes to finally add a new node. Is there a way to automate this for example using a smart contract? Then the proposal could be made automatically. I assume function modifiers could be used so that users can only propose on their own nodes.
This is not possible since the Clique PoA algorithm operates on block headers directly, which are not accessible from smart contracts.
For details see https://github.com/ethereum/EIPs/issues/225
The closest solution of the mechanism which you're describing, would be:
- a smart contract is deployed representing the permissions to seal
- sealers are calling
clique.proposeaccording to the state of the contract
However, this would only be a organisational convention and the smart contract could not enforce the changes at the protocol level. A clean solution would be to reimplement the algorithm and couple it to a pre-deployed (via genesis) smart contract.