public boolean auth()

in src/main/java/org/apache/commons/net/imap/AuthenticatingIMAPClient.java [152:210]
50 lines of code
12 McCabe index (conditional complexity)

    public boolean auth(final AuthenticatingIMAPClient.AUTH_METHOD method, final String user, final String password)
            throws IOException, NoSuchAlgorithmException, InvalidKeyException {
        if (!IMAPReply.isContinuation(sendCommand(IMAPCommand.AUTHENTICATE, method.getAuthName()))) {
            return false;
        }

        switch (method) {
        case PLAIN: {
            // the server sends an empty response ("+ "), so we don't have to read it.
            final int result = sendData(Base64.getEncoder().encodeToString(("\000" + user + "\000" + password).getBytes(getCharset())));
            if (result == IMAPReply.OK) {
                setState(IMAP.IMAPState.AUTH_STATE);
            }
            return result == IMAPReply.OK;
        }
        case CRAM_MD5: {
            // get the CRAM challenge (after "+ ")
            final byte[] serverChallenge = Base64.getDecoder().decode(getReplyString().substring(2).trim());
            // get the Mac instance
            final Mac hmacMd5 = Mac.getInstance(MAC_ALGORITHM);
            hmacMd5.init(new SecretKeySpec(password.getBytes(getCharset()), MAC_ALGORITHM));
            // compute the result:
            final byte[] hmacResult = convertToHexString(hmacMd5.doFinal(serverChallenge)).getBytes(getCharset());
            // join the byte arrays to form the reply
            final byte[] usernameBytes = user.getBytes(getCharset());
            final byte[] toEncode = new byte[usernameBytes.length + 1 /* the space */ + hmacResult.length];
            System.arraycopy(usernameBytes, 0, toEncode, 0, usernameBytes.length);
            toEncode[usernameBytes.length] = ' ';
            System.arraycopy(hmacResult, 0, toEncode, usernameBytes.length + 1, hmacResult.length);
            // send the reply and read the server code:
            final int result = sendData(Base64.getEncoder().encodeToString(toEncode));
            if (result == IMAPReply.OK) {
                setState(IMAP.IMAPState.AUTH_STATE);
            }
            return result == IMAPReply.OK;
        }
        case LOGIN: {
            // the server sends fixed responses (base64("UserName") and
            // base64("Password")), so we don't have to read them.
            if (sendData(Base64.getEncoder().encodeToString(user.getBytes(getCharset()))) != IMAPReply.CONT) {
                return false;
            }
            final int result = sendData(Base64.getEncoder().encodeToString(password.getBytes(getCharset())));
            if (result == IMAPReply.OK) {
                setState(IMAP.IMAPState.AUTH_STATE);
            }
            return result == IMAPReply.OK;
        }
        case XOAUTH:
        case XOAUTH2: {
            final int result = sendData(user);
            if (result == IMAPReply.OK) {
                setState(IMAP.IMAPState.AUTH_STATE);
            }
            return result == IMAPReply.OK;
        }
        }
        return false; // safety check
    }