Service for getting a token for editing another user's profile

[GeoffreyHuck]

fixes #1044

Encryption Algorithm

There are a few warnings on StackOverflow about using AES-128-ECB and AES-256-CBC, so the one implemented is AES-256-GCM (it includes a signature, which seems like a good idea but I don't know much about cryptography).

The most important thing for security is to make sure the nonce is always different.

Notes on the implementation:

• The result is encoded in hex
• The first 12 bytes is the nounce
• Only the first 32 bytes of the secret are used as the key, because the key must be 32 bytes for AES-256.

I'm not sure what the tag (optional) the public tag generated by the encoding (for instance in GCM) means (in the issue).

Review

Easier to review all at once. But as usual the individual commit messages contain more info.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (896e0ef) to head (7b9f3c4). Report is 3 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1086 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 237 239 +2 Lines 14329 14384 +55 ========================================= + Hits 14329 14384 +55 ```

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