A sample app to demonstrate the process of showing camera preview in web view

build.gradle

plugins {
    id 'com.android.application'
    id 'kotlin-android'
}

android {
    // Code omitted for brevity
}

dependencies {
    // Code omitted for brevity

    implementation 'androidx.activity:activity:1.2.0-rc01'
    implementation 'androidx.activity:activity-ktx:1.2.0-rc01'
    implementation 'androidx.fragment:fragment:1.3.0-rc02
}

ConfirmationDialogFragment.kt

package com.example.myapplication

import android.app.AlertDialog
import android.app.Dialog
import android.content.Context
import android.os.Bundle
import android.text.TextUtils
import androidx.fragment.app.DialogFragment

/**
Created by Prokash Sarkar on Sat, February 06, 2021
**/
class ConfirmationDialogFragment : DialogFragment() {

    companion object {
        private val ARG_RESOURCES = "resources"

        /**
         * Creates a new instance of ConfirmationDialogFragment.
         *
         * @param resources The list of resources requested by PermissionRequest.
         * @return A new instance.
         */
        fun newInstance(resources: Array<String>): ConfirmationDialogFragment {
            val fragment = ConfirmationDialogFragment()
            val args = Bundle()
            args.putStringArray(ARG_RESOURCES, resources)
            fragment.arguments = args
            return fragment
        }
    }

    private lateinit var webPermissionListener: WebPermissionListener

    override fun onAttach(context: Context) {
        super.onAttach(context)
        webPermissionListener = context as WebPermissionListener
    }

    override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
        val resources = arguments?.getStringArray(ARG_RESOURCES)
        return AlertDialog.Builder(activity)
            .setMessage(getString(R.string.confirmation, TextUtils.join("\n", resources!!)))
            .setNegativeButton(R.string.deny) { dialog, which ->
                webPermissionListener.onConfirmation(false, resources)
            }
            .setPositiveButton(R.string.allow) { dialog, which ->
                webPermissionListener.onConfirmation(true, resources)
            }
            .create()
    }

    /**
     * Callback for the user's response.
     */
    interface WebPermissionListener {
        /**
         * Called when the PermissionRequest is allowed or denied by the user.
         *
         * @param allowed   True if the user allowed the request.
         * @param resources The resources to be granted.
         */
        fun onConfirmation(allowed: Boolean, resources: Array<String?>?)
    }

}

manifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.myapplication">

    <uses-permission android:name="android.permission.CAMERA" />

    <uses-feature android:name="android.hardware.camera" />
    <uses-feature android:name="android.hardware.camera.autofocus" />

    <uses-permission android:name="android.permission.INTERNET"/>

    // Code omitted for brevity

</manifest>

WebViewActivity.kt

package com.example.myapplication

import android.Manifest
import android.annotation.SuppressLint
import android.content.pm.PackageManager
import android.os.Build
import android.os.Bundle
import android.webkit.*
import android.widget.Toast
import androidx.activity.result.ActivityResultLauncher
import androidx.activity.result.contract.ActivityResultContracts
import androidx.appcompat.app.AppCompatActivity
import androidx.core.content.ContextCompat
import androidx.fragment.app.DialogFragment

/**
Created by Prokash Sarkar on Sat, February 06, 2021
**/
class WebViewActivity : AppCompatActivity(), ConfirmationDialogFragment.WebPermissionListener {

    private lateinit var webView: WebView

    private val URL = "replace_with_your_url"

    /**
     * This field stores the [PermissionRequest] from the web application until it is allowed
     * or denied by user.
     */
    private var mPermissionRequest: PermissionRequest? = null

    private val FRAGMENT_DIALOG = "dialog"

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        webView = findViewById(R.id.webview)
        webView.webViewClient = webViewClient
        webView.webChromeClient = webChromeClient
      
        configureWebSettings()
      
        checkForRequiredPermissions()
    }

    @SuppressLint("SetJavaScriptEnabled")
    private fun configureWebSettings() {
        webView.settings.apply {
            javaScriptEnabled = true
            domStorageEnabled = true
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
                mediaPlaybackRequiresUserGesture = false
            }
        }
    }

    private val webViewClient = object : WebViewClient() {
        override fun shouldOverrideUrlLoading(view: WebView?, request: WebResourceRequest?): Boolean {
            view?.loadUrl(request?.url.toString())
            return true
        }
    }

    private val webChromeClient = object : WebChromeClient() {
        override fun onPermissionRequest(request: PermissionRequest?) {
            println("onPermissionRequest")
            mPermissionRequest = request
            request?.resources?.let {
                for (r in it) {
                    if (r == PermissionRequest.RESOURCE_VIDEO_CAPTURE) {
                        // In this sample, we only accept video capture request.
                        ConfirmationDialogFragment
                                .newInstance(arrayOf(PermissionRequest.RESOURCE_VIDEO_CAPTURE))
                                .show(supportFragmentManager, FRAGMENT_DIALOG)
                        break
                    }
                }
            }
        }

        override fun onPermissionRequestCanceled(request: PermissionRequest?) {
            println("onPermissionRequestCanceled")
            mPermissionRequest = null
            val fragment: DialogFragment = supportFragmentManager.findFragmentByTag(FRAGMENT_DIALOG) as DialogFragment
            fragment.dismiss()
        }
    }

    private fun checkForRequiredPermissions() {
        val requestPermissionLauncher: ActivityResultLauncher<String> =
                registerForActivityResult(ActivityResultContracts.RequestPermission()) { isGranted: Boolean ->
                    if (isGranted) {
                        // Permission is granted. Continue the action or workflow in your app.
                        Toast.makeText(this, "Camera Permission Granted", Toast.LENGTH_SHORT).show()
                        webView.loadUrl(URL)
                    } else {
                        // Explain to the user that the feature is unavailable
                        Toast.makeText(this, "Camera Permission Denied", Toast.LENGTH_SHORT).show()
                    }
                }

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            when {
                ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA)
                        == PackageManager.PERMISSION_GRANTED -> {
                    // You can use the API that requires the permission.
                    Toast.makeText(this, "Camera Permission already Granted", Toast.LENGTH_SHORT)
                            .show()
                    webView.loadUrl(URL)
                }
                shouldShowRequestPermissionRationale(Manifest.permission.CAMERA) -> {
                    // In an educational UI, explain to the user why your app requires this
                    Toast.makeText(
                            this,
                            "Camera Permission is required to use the app",
                            Toast.LENGTH_SHORT
                    ).show()
                }
                else -> {
                    requestPermissionLauncher.launch(Manifest.permission.CAMERA)
                }
            }
        }
    }

    override fun onConfirmation(allowed: Boolean, resources: Array<String?>?) {
        if (allowed) {
            mPermissionRequest!!.grant(resources)
            println("Permission granted.")
        } else {
            mPermissionRequest!!.deny()
            println("Permission denied.")
        }
        mPermissionRequest = null
    }

}