A sample script to show how to set the signature block of a member of your domain
####1) You will need to add the library: MswhXl8fVhTFUH_Q3UOJbXvxhMjh3Sh48
####2) In the project's developer console enable the api: admin sdk
####3) Set up the project credentials as an Oauth Web Application: Authorized JavaScript origins: https://script.google.com
Authorized redirect URIs: https://script.google.com/macros/d/{PROJECT KEY}/usercallback
note: the project key can be found in you scripts File-> Project Properties ####4) Add the generated Client Id and Client Secret: Add the script properties clientId and clientSecret and add their respective values from the generated credentials
####5) Add the {project key} AdminOauth2.gs: on the line .setProjectKey('...') add the project key
####6) Publish the script as a webapp. You will need to authorize the app first by running the authScript() function. Next browse to the web-app url to authorize access to you domains email settings The call to make the signatuire will look like the test() function.
Read the docs of the Oauth2 library at: https://github.com/googlesamples/apps-script-oauth2