D4Sign
D4Sign is an electronic document signature platform that meets the requirements of Brazilian Provisional Measure 2.200-2/01, that is, authenticity, integrity and non-repudiation.
Environments
D4Sign offers a test environment (Sandbox). You can test the integration by creating an account in that environment at https://sandbox.d4sign.com.br/.
Get the API Key
To get your API Key, go to D4Sign > (your e-mail) > Dev (API), as shown in the image below:

Then you must copy the tokenAPI and the cryptKey:

Enter the information in NicoChat
In NicoChat, go to NicoApps and look for the D4Sign app. Install the app and enter the data you obtained:
