Using OAuth to access Mail Services

OAuth 2.0 support has been added to Aspose.Email and can be used to access SMTP, POP3, IMAP and EWS servers. In general, all servers supporting OAuth 2.0 bearer tokens can be used with Aspose.Email, but our email clients have been tested with Google mail servers and Microsoft Office 365 servers. Access to the server from the SmtpClient, Pop3Client, ImapClient and EWSClient with OAuth may be implemented in 2 ways.

  1. Provide access token directly into the constructor of email client. In this case, the user has to understand that lifetime of access tokens is limited. When the token is expired, email client can’t be used to access the server.
  2. Provide a custom implementation of token provider based on ITokenProvider interface into the constructor of email client. In this case, the client checks token expiration time and requests ITokenProvider for a new access token when the previous is expired. In this way, the client refreshes tokens periodically and may work with the server for unlimited time. Š˛ften services support a simple way to refresh access tokens. For example, using refresh tokens in google services or ROPC authentication flow in Microsoft identity platform can be used for implementation token provider.

Configure an Account on the Appropriate Server

The following articles help you to configure accounts to access mail services.

Access Mail Services with the Access Tokens

The following code examples show you how to connect to mail services using access tokens.

// Connecting to SMTP server
try (SmtpClient client = new SmtpClient(
        "smtp.gmail.com",
        587,
        "user1@gmail.com",
        "accessToken",
        true,
        SecurityOptions.SSLExplicit)) {

}

// Connecting to IMAP server
try (ImapClient client = new ImapClient(
        "imap.gmail.com",
        993,
        "user1@gmail.com",
        "accessToken",
        true,
        SecurityOptions.SSLImplicit)) {

}

// Connecting to POP3 server
try (Pop3Client client = new Pop3Client(
        "pop.gmail.com",
        995,
        "user1@gmail.com",
        "accessToken",
        true,
        SecurityOptions.Auto)) {

}

Access Mail Services with the Token Providers

The following code examples show you how to connect to mail services using a token provider.

ITokenProvider tokenProvider = TokenProvider.Google.getInstance(
        "ClientId",
        "ClientSecret",
        "RefreshToken");

// Connecting to SMTP server
try (SmtpClient client = new SmtpClient(
        "smtp.gmail.com",
        587,
        "user1@gmail.com",
        tokenProvider,
        SecurityOptions.SSLExplicit)) {

}

// Connecting to IMAP server
try (ImapClient client = new ImapClient(
        "imap.gmail.com",
        993,
        "user1@gmail.com",
        tokenProvider,
        SecurityOptions.SSLImplicit)) {

}

// Connecting to POP3 server
try (Pop3Client client = new Pop3Client(
        "pop.gmail.com",
        995,
        "user1@gmail.com",
        tokenProvider,
        SecurityOptions.Auto)) {

}

Implementation of Custom ITokenProvider for Office 365

You can use the token provider implementation below to access Office 365 mail services.

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLDecoder;
import java.net.URLEncoder;
import java.nio.charset.StandardCharsets;
import java.util.HashMap;
import java.util.Map;

/**
 * <p>
 * Azure resource owner password credential (ROPC) token provider
 * https://docs.microsoft.com/en-us/azure/active-directory/develop/v2-oauth-ropc
 * https://docs.microsoft.com/en-us/exchange/client-developer/exchange-web-services/how-to-authenticate-an-ews-application-by-using-oauth
 * https://portal.azure.com
 * https://developer.microsoft.com/en-us/graph/graph-explorer/#
 * token parser https://jwt.io
 * </p>
 */
class AzureROPCTokenProvider implements ITokenProvider {

    private static final String GRANT_TYPE = "password";

    private final String clientId;
    private final String clientSecret;
    private final String userName;
    private final String password;
    private final String tenant;
    private final String scope;

    private OAuthToken token;

    public AzureROPCTokenProvider(String tenant, String clientId, String clientSecret,
                                  String userName, String password, String[] scopeAr) {
        this.tenant = tenant;
        this.clientId = clientId;
        this.clientSecret = clientSecret;
        this.userName = userName;
        this.password = password;
        this.scope = joinToStr(scopeAr, " ");
    }

    public synchronized OAuthToken getAccessToken(boolean ignoreExistingToken) {
        if (this.token != null && !this.token.getExpired() && !ignoreExistingToken)
            return this.token;
        token = null;

        Map<String, String> tokenArgs = geToken();

        java.util.Calendar c = java.util.Calendar.getInstance();
        c.add(java.util.Calendar.SECOND, Integer.parseInt(tokenArgs.get("expires_in")));
        token = new OAuthToken(tokenArgs.get("access_token"), TokenType.AccessToken, c.getTime());
        return token;
    }

    public final OAuthToken getAccessToken() {
        return getAccessToken(false);
    }

    public void dispose() {
    }

    private String getEncodedParameters() {
        return "client_id=" + urlEncode(clientId) + "&scope=" + urlEncode(scope) + "&username=" + urlEncode(userName)
                + "&password=" + urlEncode(password) + "&grant_type="
                + urlEncode(GRANT_TYPE);
    }

    private String getUri() {
        if (tenant == null || tenant.trim().isEmpty())
            return "https://login.microsoftonline.com/common/oauth2/v2.0/token";
        else
            return "https://login.microsoftonline.com/" + tenant + "/oauth2/v2.0/token";
    }

    private Map<String, String> geToken() {
        try {
            HttpURLConnection connection = (HttpURLConnection) new URL(getUri()).openConnection();
            connection.setRequestMethod("POST");

            byte[] requestData = getEncodedParameters().getBytes(StandardCharsets.UTF_8);

            connection.setUseCaches(false);
            connection.setDoInput(true);
            connection.setDoOutput(true);
            connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
            connection.setRequestProperty("Content-Length", "" + requestData.length);

            final OutputStream st = connection.getOutputStream();
            try {
                st.write(requestData, 0, requestData.length);
            } finally {
                st.flush();
                st.close();
            }

            connection.connect();

            if (connection.getResponseCode() >= HttpURLConnection.HTTP_BAD_REQUEST) {
                throw new IllegalAccessError("Operation failed: " + connection.getResponseCode() + "/" +
                        connection.getResponseMessage() + "\r\nDetails:\r\n{2}"
                        + readInputStream(connection.getErrorStream()));
            }

            String responseText = readInputStream(connection.getInputStream());

            Map<String, String> result = new HashMap<>();
            String[] fromJsonToKeyValue = responseText.replace("{", "").replace("}", "")
                    .replace("\"", "").replace("\r", "")
                    .replace("\n", "").split(",");
            for (String keyValue : fromJsonToKeyValue) {
                String[] pair = keyValue.split(":");
                String name = pair[0].trim().toLowerCase();
                String value = urlDecode(pair[1].trim());
                result.put(name, value);
            }

            return result;
        } catch (IOException e) {
            throw new IllegalAccessError(e.getMessage());
        }
    }

    static String urlEncode(String value) {
        try {
            return URLEncoder.encode(value, StandardCharsets.UTF_8.toString());
        } catch (UnsupportedEncodingException e) {
            throw new IllegalAccessError(e.getMessage());
        }
    }

    static String urlDecode(String value) {
        try {
            return URLDecoder.decode(value, StandardCharsets.UTF_8.toString());
        } catch (UnsupportedEncodingException e) {
            throw new IllegalAccessError(e.getMessage());
        }
    }

    static String readInputStream(InputStream is) {
        if (is == null)
            return "";

        BufferedReader reader = new BufferedReader(new InputStreamReader(is));
        StringBuilder result = new StringBuilder();
        String line;
        try {
            while ((line = reader.readLine()) != null) {
                result.append(line);
            }
        } catch (IOException e) {
            // ignore
        }
        return result.toString();
    }

    static String joinToStr(String[] arr, String sep) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < arr.length; i++) {
            if (i > 0)
                sb.append(sep);
            sb.append(arr[i]);
        }
        return sb.toString();
    }
}

The next code examples show you how to connect to Office 365 services using the custom token provider.

ITokenProvider tokenProvider = new AzureROPCTokenProvider(
        "Tenant",
        "ClientId",
        "ClientSecret",
        "EMail",
        "Password",
        scopes);

// Connecting to SMTP server
try (SmtpClient client = new SmtpClient(
        "smtp.office365.com",
        587,
        "Test1@test.onmicrosoft.com",
        tokenProvider,
        SecurityOptions.SSLExplicit)) {

}

// Connecting to IMAP server
try (ImapClient client = new ImapClient(
        "outlook.office365.com",
        993,
        "Test1@test.onmicrosoft.com",
        tokenProvider,
        SecurityOptions.SSLImplicit)) {

}

// Connecting to POP3 server
try (Pop3Client client = new Pop3Client(
        "outlook.office365.com",
        995,
        "Test1@test.onmicrosoft.com",
        tokenProvider,
        SecurityOptions.Auto)) {

}

// Connecting to EWS server
final String mailboxUri = "https://outlook.office365.com/ews/exchange.asmx";
ICredentials credentials = new OAuthNetworkCredential(tokenProvider);
try (IEWSClient ewsClient = EWSClient.getEWSClient(mailboxUri, credentials)) {

}

Permissions to access Office 365 via IMAP, POP3 or SMTP

We need to apply correct API permissions and grant the admin consent to access Office 365 mail services:

todo:image_alt_text

In the API permissions / Add a permission wizard, select Microsoft Graph and then Delegated permissions to find the following permission scopes listed:

offline_access
IMAP.AccessAsUser.All
POP.AccessAsUser.All
SMTP.Send

Token provider Example:

ITokenProvider tokenProvider = new AzureROPCTokenProvider(OAuth.Tenant, OAuth.ClientId, OAuth.ClientSecret, User.EMail, User.Password,
        new String[] {
                "offline_access",
                "https://outlook.office.com/IMAP.AccessAsUser.All", // IMAP scope
                "https://outlook.office.com/POP.AccessAsUser.All",  // POP3 scope
                "https://outlook.office.com/SMTP.Send"              // SMTP scope
        });