(C) Refresh GMail SMTP OAuth2 Access Token

Demonstrates how to refresh an access token for sending email via GMail (SMTP).

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#include <C_CkJsonObject.h>
#include <C_CkOAuth2.h>
#include <C_CkStringBuilder.h>

void ChilkatSample(void)
    {
    HCkJsonObject jsonToken;
    BOOL success;
    HCkOAuth2 oauth2;
    HCkStringBuilder sbJson;

    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // See Get GMail SMTP Access Token 
    // for sample code showing how to obtain a GMail SMTP access token for desktop apps.

    // It is assumed we previously obtained an OAuth2 access token for GMail (one with a scope for sending email).

    jsonToken = CkJsonObject_Create();
    success = CkJsonObject_LoadFile(jsonToken,"qa_data/tokens/_gmailSmtp.json");
    if (success != TRUE) {
        printf("Failed to load _gmailSmtp.json\n");
        CkJsonObject_Dispose(jsonToken);
        return;
    }

    // The access token JSON looks something like this:

    // 	{ 
    // 	 "access_token": "abac.Ci-ZabcdF37-NUrmSzxbHxTsMbtlN-uPfabcdAQN_2ekzj0s5ofCzRabcdTDMGaa2Q",
    // 	 "token_type": "Bearer",
    // 	 "expires_in": 3600,
    // 	 "refresh_token": "1/lEe5abcdNJ77eOSDBabcdkQGVmDalkwabcdR2Hatbo"
    // 	}
    // 

    oauth2 = CkOAuth2_Create();

    CkOAuth2_putTokenEndpoint(oauth2,"https://www.googleapis.com/oauth2/v4/token");

    // Replace these with actual values.
    CkOAuth2_putClientId(oauth2,"GOOGLE-CLIENT-ID");
    CkOAuth2_putClientSecret(oauth2,"GOOGLE-CLIENT-SECRET");

    // Get the "refresh_token"
    CkOAuth2_putRefreshToken(oauth2,CkJsonObject_stringOf(jsonToken,"refresh_token"));

    // Send the HTTP POST to refresh the access token..
    success = CkOAuth2_RefreshAccessToken(oauth2);
    if (success != TRUE) {
        printf("%s\n",CkOAuth2_lastErrorText(oauth2));
        CkJsonObject_Dispose(jsonToken);
        CkOAuth2_Dispose(oauth2);
        return;
    }

    // The response contains a new access token, but we must keep
    // our existing refresh token for when we need to refresh again in the future.
    CkJsonObject_UpdateString(jsonToken,"access_token",CkOAuth2_accessToken(oauth2));

    // Save the new JSON access token response to a file.
    sbJson = CkStringBuilder_Create();
    CkJsonObject_putEmitCompact(jsonToken,FALSE);
    CkJsonObject_EmitSb(jsonToken,sbJson);
    CkStringBuilder_WriteFile(sbJson,"qa_data/tokens/_gmailSmtp.json","utf-8",FALSE);

    printf("OAuth2 authorization granted!\n");
    printf("New Access Token = %s\n",CkOAuth2_accessToken(oauth2));


    CkJsonObject_Dispose(jsonToken);
    CkOAuth2_Dispose(oauth2);
    CkStringBuilder_Dispose(sbJson);

    }