Using TLS with Oracle Call Interface connections with newer Oracle Instant Client/Oracle Database Client versions, a wallet is not required. For TLS connections with Oracle Call Interface running on older Oracle Instant Client/Oracle Database Client versions, a wallet is required for both mTLS authenticated connections and TLS authenticated connections.

• Oracle Call Interface (OCI) Connections and Wallets (mTLS)
  Oracle Net Services can find the location of the Autonomous Database wallet using the WALLET_LOCATION parameter in the sqlnet.ora file.
• Oracle Call Interface (OCI) Connections with TLS Authentication
  Using TLS with Oracle Call Interface, connections with newer Oracle Instant Client/Oracle Database Client versions, a wallet is not required.