Here is a way of implementing pairing/bonding with RxAndroidBle

PairingManager.kt

package hello.world

import android.bluetooth.BluetoothDevice
import android.content.Context
import android.content.Intent
import android.content.IntentFilter
import android.content.BroadcastReceiver
import com.polidea.rxandroidble2.RxBleDevice
import io.reactivex.Completable
import io.reactivex.disposables.Disposables

/**
 * Created by clement on 2017-08-24.
 */

class PairingFailedException : RuntimeException()

internal object PairingManager {

    /**
     * @throws PairingFailedException
     */
    // TODO: try to understand why the popup is being displayed in the notification center (sometimes) ???!!!
    fun pairWithDevice(context: Context, rxBleDevice: RxBleDevice): Completable {

        return Completable.create { completion ->

            when (rxBleDevice.bluetoothDevice.bondState) {
                BluetoothDevice.BOND_BONDED -> completion.onComplete()
                else -> {

                    val receiver = object : BroadcastReceiver() {
                        override fun onReceive(context: Context, intent: Intent) {
                            val deviceBeingPaired = intent.getParcelableExtra<BluetoothDevice>(BluetoothDevice.EXTRA_DEVICE)

                            if (deviceBeingPaired.address == rxBleDevice.bluetoothDevice.address) {
                                val state = intent.getIntExtra(BluetoothDevice.EXTRA_BOND_STATE, BluetoothDevice.BOND_NONE)

                                when (state) {
                                    BluetoothDevice.BOND_BONDED -> completion.onComplete()
                                    BluetoothDevice.BOND_NONE -> completion.tryOnError(PairingFailedException())
                                }
                            }
                        }
                    }

                    completion.setDisposable(Disposables.fromAction { context.unregisterReceiver(receiver) })

                    context.registerReceiver(receiver, IntentFilter(BluetoothDevice.ACTION_BOND_STATE_CHANGED))

                    val createBondResult = rxBleDevice.bluetoothDevice.createBond()

                    if (createBondResult == false) {
                        completion.tryOnError(PairingFailedException())
                    }

                }
            }

        }

    }

}

And Then

return PairingManager
  .pairWithDevice(this.context, rxBleDevice)
  .andThen(connectToBleDevice)

@RobLewis

Java version (with lambda)

    public static class PairingFailedException extends RuntimeException {
    }

    
    public static Completable pairWithDevice(final Context context, final RxBleDevice rxBleDevice) {
        return Completable.create(completion -> {
            if (rxBleDevice.getBluetoothDevice().getBondState() == BluetoothDevice.BOND_BONDED) {
                completion.onComplete();
                return;
            }

            final BroadcastReceiver receiver = new BroadcastReceiver() {
                @Override
                public void onReceive(final Context context, final Intent intent) {
                    final BluetoothDevice deviceBeingPaired = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);

                    if (deviceBeingPaired.getAddress().equals(rxBleDevice.getBluetoothDevice().getAddress())) {
                        final int state = intent.getIntExtra(BluetoothDevice.EXTRA_BOND_STATE, BluetoothDevice.BOND_NONE);

                        if (state == BluetoothDevice.BOND_BONDED) {
                            completion.onComplete();
                            abortBroadcast();
                        } else if (state == BluetoothDevice.BOND_NONE) {
                            completion.tryOnError(new PairingFailedException());
                            abortBroadcast();
                        }
                    }
                }
            };

            completion.setDisposable(Disposables.fromAction(() -> context.unregisterReceiver(receiver)));
            context.registerReceiver(receiver, new IntentFilter(BluetoothDevice.ACTION_BOND_STATE_CHANGED));
            
            final boolean createBondResult = rxBleDevice.getBluetoothDevice().createBond();
            if (!createBondResult) {
                completion.tryOnError(new PairingFailedException());
            }
        });
    }