Shared Secret can be a:
Shared Secret is either shared beforehand between the communicating parties, in which case it can also be called a pre-shared key, or it is created at the start of the communication session by using a Key-Exchange protocol, for instance using Public Key cryptography such as Diffie-Hellman or using Symmetric Key cryptography such as Kerberos.
Shared Secret can be used for authentication using methods such as challenge-response or it can be fed to a key derivation function to produce one or more keys to use for encryption and/or MACing of messages.
More Information#There might be more information for this subject on one of the following:
- Mutual TLS Profiles for OAuth Clients
- Password Authentication is Broken
- Pre-shared key
- Time-based One-time Password Algorithm