Sign data and provide a base64 signature

[danielfttorres]

Expected Behavior

The user must be able to sign data and receive a valid base64 signature in a single line, e.g.:

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

Checklist

• Add native sign method
• Create a bridge fot the method
• Document the method

[danielfttorres]

On Android: #4