How can data be added to a group and retrieved only by its members?

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One way to add data to a group and retrieve it only by its members is to use encryption and access control mechanisms.

First, the data can be encrypted using a unique key that is only known to the members of the group. The encrypted data can then be stored in a database or other storage solution.

To retrieve the data, a member of the group must provide their authorization credentials, such as a username and password, to access the data. The access control mechanism can verify that the member is authorized to access the data by checking their credentials against a list of authorized users for the group.

Once the member is authenticated, the decryption key can be provided, allowing the member to access the data in its decrypted form. This ensures that only authorized members of the group can access the data, and that the data remains secure and private.