Zig

Get Google API Access Token using JSON Private Key

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Demonstrates how to get a Google API access token using a JSON service account private key. Zig

const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

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

    // --------------------------------------------------------------------------------
    // For a step-by-step guide for setting up your Google Workspace service account,
    // see Setup Google Workspace Account for Sending SMTP GMail from a Service Account
    // --------------------------------------------------------------------------------

    // First load the JSON key into a string.
    const fac = try chilkat.FileAccess.init();
    defer fac.deinit();
    const json_key = fac.readEntireTextFile(alloc, "qa_data/googleApi/chilkat25-b4214220e565.json", "utf-8") catch {
        std.debug.print("{s}\n", .{try fac.getLastErrorText(alloc)});
        return;
    };

    // A Google service account JSON private key looks like this:

    // {
    //   "type": "service_account",
    //   "project_id": "chilkat25",
    //   "private_key_id": "b4214220f565881e19eeb97c2699bf5a0d1e3e0b",
    //   "private_key": "-----BEGIN PRIVATE KEY-----\nMIIEvQ...NXcM=\n-----END PRIVATE KEY-----\n",
    //   "client_email": "chilkatsvc@chilkat25.iam.gserviceaccount.com",
    //   "client_id": "109122032928932715958",
    //   "auth_uri": "https://accounts.google.com/o/oauth2/auth",
    //   "token_uri": "https://oauth2.googleapis.com/token",
    //   "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
    //   "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/chilkatsvc%40chilkat25.iam.gserviceaccount.com",
    //   "universe_domain": "googleapis.com"
    // }

    const g_auth = try chilkat.AuthGoogle.init();
    defer g_auth.deinit();
    g_auth.setJsonKey(json_key);

    // Specify a scope.
    g_auth.setScope("https://mail.google.com/");

    // Request an access token that is valid for this many seconds.
    g_auth.setExpireNumSeconds(3600);

    // When using a Google Workspace account with Gmail APIs, a service account can impersonate a user
    // via a process called domain-wide delegation — and the "sub" claim in the JWT is what enables this.
    // Domain-wide delegation allows a Google Workspace administrator to authorize a service account to
    // act on behalf of any user in the domain, without user interaction.

    // This is required for server-to-server access to user data — such as reading/sending Gmail from a background service.
    // This is your company email address.
    g_auth.setSubEmailAddress("info@chilkat.xyz");

    // Connect to www.googleapis.com using TLS
    const tls_sock = try chilkat.Socket.init();
    defer tls_sock.deinit();
    tls_sock.connect("www.googleapis.com", 443, true, 5000) catch {
        std.debug.print("{s}\n", .{try tls_sock.getLastErrorText(alloc)});
        return;
    };

    // Send the request to obtain the access token.
    g_auth.obtainAccessToken(tls_sock) catch {
        std.debug.print("{s}\n", .{try g_auth.getLastErrorText(alloc)});
        return;
    };

    // Examine the access token:
    const access_token = try g_auth.getAccessToken(alloc);
    std.debug.print("Access Token: {s}\n", .{access_token});

    // Sample output:
    // ya29.a0AW4XtxjGTD67Z8 .... IRw0218

    // The access token allows us to send unlimited emails while it's valid. Once it expires, we must obtain and use a new one.

    // -----------------------------------------------------------------------
    const mailman = try chilkat.MailMan.init();
    defer mailman.deinit();

    // Set the properties for the GMail SMTP server:
    mailman.setSmtpHost("smtp.gmail.com");
    mailman.setSmtpPort(587);
    mailman.setStartTLS(true);

    mailman.setSmtpUsername("info@chilkat.xyz");
    mailman.setOAuth2AccessToken(access_token);

    // Create a new email object
    const email = try chilkat.Email.init();
    defer email.deinit();

    email.setSubject("This is a test");
    email.setBody("This is a test");
    email.setFrom("Chilkat Test <info@chilkat.xyz>");
    try email.addTo("Chilkat Software", "info@chilkatsoft.com");
    // To add more recipients, call AddTo, AddCC, or AddBcc once per recipient.

    mailman.sendEmail(email) catch {
        std.debug.print("{s}\n", .{try mailman.getLastErrorText(alloc)});
        return;
    };

    mailman.closeSmtpConnection() catch {
        std.debug.print("Connection to SMTP server not closed cleanly.\n", .{});
    };

    std.debug.print("Successfully sent email using Gmail with a service account key.\n", .{});
}