The wallet itself comes with its own secret key when it generates the wallet keys.
Creating wallet: default
Save password to use in the future to unlock this wallet.
Without password imported keys will not be retrievable.
This key will be used to unlock your wallet to import additional keys into your wallet. You may use ...
I have found a solution, but I am unsure if this is the right way to do it.
The included files were under /usr/opt/eosio.cdt/1.6.1/include/eosiolib/contracts/eosio/
From there, it seems that the file transaction.hpp is included only in permission.hpp, but permission.hpp is not included anywhere:
[***** addressbook]$ grep -HiR "transaction.hpp" /usr/opt/...
Best is EOS Authority's portal:
They have a video as well:
The architecture of the contract is so that you cannot lose your initial input unless the contract is somehow hacked. When you stake to REX your balance will lower in blocks for your staked CPU amount. You receive REX ...
Probably the best tutorial is to take a look at the Universal Authenticator Library - UAL and how it works.
Here are some helpful links:
Medium Article about the UAL
UAL Authenticator Walkthrough
There are are several different UAL-Repositories + Usage-Examples for use with the different available Wallets.