ERROR:
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ora-28040 no matching authentication protocol in 12C
SOLUTION:
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1. Edit the sqlnet.ora file of the 12c database.
2. Remove or comment the following entry.
SQLNET.ALLOWED_LOGON_VERSION
3. Add the following two new Oracle Net Services parameters:
SQLNET.ALLOWED_LOGON_VERSION_SERVER
SQLNET.ALLOWED_LOGON_VERSION_CLIENT
4. Bounce the database.
5. Bounce the application server.