(Java) Office365 Refresh OAuth2 Access Token for SMTP, IMAP, POP

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Demonstrates how to refresh an Office365 OAuth2 access token for use in the SMTP, IMAP, and POP3 protocols.

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import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // It is assumed we previously obtained an OAuth2 access token.
    // This example loads the JSON access token file 
    // saved by this example: Get Office365 SMTP/IMAP/POP3 OAuth2 Access Token

    // Note: Refreshing an access token does not require user-interaction.  
    // Only the act of getting the initial access token requires interactive authorization from the Office365 account owner 
    // (i.e. a browser is displayed and the account owner authorizes access by the app).

    // Once you have the initial access token, it can be refreshed over and over again with no limits.
    // A typical strategy is to write your application to automatically refresh the access token 
    // when authentication fails, and then retry the operation with the new access token.
    // For example, see Auto-Refresh O365 Access Token when Sending Email

    CkJsonObject jsonToken = new CkJsonObject();
    boolean success = jsonToken.LoadFile("qa_data/tokens/office365.json");
    if (success != true) {
        System.out.println("Failed to load office365.json");
        return;
        }

    // The access token JSON looks like this:

    // {
    //   "token_type": "Bearer",
    //   "scope": "IMAP.AccessAsUser.All openid POP.AccessAsUser.All profile SMTP.Send email",
    //   "expires_in": 3599,
    //   "ext_expires_in": 3599,
    //   "access_token": "...",
    //   "refresh_token": "...",
    //   "id_token": "...",
    //   "expires_on": "1592748507"
    // }

    CkOAuth2 oauth2 = new CkOAuth2();

    // Update to use your token endpoint.
    // In the Azure Portal, in "App registrations", go to "Endpoints" (located to the right of the "+ New registration" link.)
    //    Find your endpoint for the "OAuth 2.0 token endpoint (v2)"
    //    See Office365 OAuth2 Endpoints

    oauth2.put_TokenEndpoint("https://login.microsoftonline.com/xxxxxxxxxx-71bf-4ebe-a866-738364321bf2/oauth2/v2.0/token");

    // Replace these with actual values.
    oauth2.put_ClientId("CLIENT_ID");
    oauth2.put_ClientSecret("CLIENT_SECRET");

    // Get the "refresh_token"
    oauth2.put_RefreshToken(jsonToken.stringOf("refresh_token"));

    // Send the HTTP POST to refresh the access token..
    success = oauth2.RefreshAccessToken();
    if (success != true) {
        System.out.println(oauth2.lastErrorText());
        return;
        }

    System.out.println("New access token: " + oauth2.accessToken());
    System.out.println("New refresh token: " + oauth2.refreshToken());

    // Update the JSON with the new tokens.
    jsonToken.UpdateString("access_token",oauth2.accessToken());
    jsonToken.UpdateString("refresh_token",oauth2.refreshToken());

    // Save the new JSON access token response to a file.
    CkStringBuilder sbJson = new CkStringBuilder();
    jsonToken.put_EmitCompact(false);
    jsonToken.EmitSb(sbJson);
    sbJson.WriteFile("qa_data/tokens/office365.json","utf-8",false);

    System.out.println("OAuth2 authorization granted!");
    System.out.println("New Access Token = " + oauth2.accessToken());
  }
}