We can read data from Oracle or MSSQL with the help of PostgreSQL Foreign Data Wrapper. Please read the following articles for installation and detailed information.
You have created oracle_fdw(Oracle Foreign Data Wrapper Extension) or tds_fdw(MSSQL Foreign Data Wrapper Extension) in the PostgreSQL Cluster. In order to enable the application developer to perform his / her own operations on Oracle_fdw or tds_fdw, you can authorize the user as follows.
GRANT ALL ON FOREIGN DATA WRAPPER oracle_fdw FROM pg_User
GRANT ALL ON FOREIGN DATA WRAPPER tds_fdw FROM pg_User;