How to install cryptography extension libsodium for php7.0.27

After trying to install this extension using pecl without much success,

I had the following message:  “Warning cannot install module.These settings must match”.
To summarize, the pecl extension was not compiled with the right version of php.

The short tutorial I show you here works well and have been tested on 
Ubuntu Server 16.04 LTS and php7.0.27.

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