I am trying to learn Firebase, so I went through the Android Codelab. The project they gave me however, had an error:
Cannot resolve symbol default_web_cl
Generic solution for this is to apply google play services plugin at the end of build.gradle like this
  apply plugin: 'com.android.application'
android {
    compileSdkVersion 30
    buildToolsVersion "30.0.0"
    buildFeatures {
        dataBinding true
    }
    defaultConfig {
        applicationId "xxxxxx"
        minSdkVersion 21
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"
        multiDexEnabled true
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}
dependencies {
    implementation fileTree(dir: "libs", include: ["*.jar"])
    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.13'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
    // For Common Dimension
    implementation 'com.intuit.sdp:sdp-android:1.0.5'
    implementation 'com.intuit.ssp:ssp-android:1.0.5'
    // Retrofit and Gson
    implementation 'com.google.code.gson:gson:2.8.6'
    implementation 'com.squareup.retrofit2:retrofit:2.6.1'
    implementation 'com.squareup.retrofit2:converter-gson:2.3.0'
    implementation 'com.squareup.retrofit2:converter-scalars:2.6.1'
    // Rx Java and Dagger
    implementation 'com.squareup.retrofit2:adapter-rxjava:2.1.0'
    implementation 'io.reactivex:rxandroid:1.2.1'
    implementation 'io.reactivex:rxjava:1.1.6'
    implementation 'com.google.dagger:dagger:2.24'
    annotationProcessor 'com.google.dagger:dagger-compiler:2.24'
    compileOnly 'javax.annotation:jsr250-api:1.0'
    compileOnly 'org.glassfish:javax.annotation:10.0-b28'
    // Glide Image Loading
    implementation 'com.github.bumptech.glide:glide:4.9.0'
    annotationProcessor 'com.github.bumptech.glide:compiler:4.7.1'
    implementation 'com.android.support:design:30.0.0'
    implementation 'com.android.support:recyclerview-v7:30.0.0'
    implementation 'com.android.support:cardview-v7:30.0.0'
    implementation 'com.android.support:multidex:1.0.3'
    /*Jsoup*/
    implementation 'org.jsoup:jsoup:1.9.1'
    /*Firebase*/
    implementation 'com.google.firebase:firebase-core:17.5.0'
    implementation 'com.google.firebase:firebase-config:19.2.0'
    implementation 'com.google.firebase:firebase-messaging:20.2.4'
    implementation 'com.google.firebase:firebase-database:19.3.1'
    implementation 'com.google.firebase:firebase-auth:19.3.2'
    implementation 'com.firebaseui:firebase-ui-storage:6.2.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    implementation 'com.google.firebase:firebase-analytics:17.5.0'
    /*location and google map*/
    implementation 'com.google.android.gms:play-services-maps:17.0.0'
    implementation 'com.google.android.gms:play-services-location:17.0.0'
    implementation 'com.google.android.gms:play-services-places:17.0.0'
    implementation 'com.google.android.gms:play-services-auth:18.1.0'
    /*Circle Image View*/
    implementation 'de.hdodenhof:circleimageview:3.0.1'
    implementation 'com.github.ittianyu:BottomNavigationViewEx:2.0.4'
    implementation "com.android.support:design:30.0.0"
    implementation 'com.facebook.android:facebook-android-sdk:5.15.3'
}
apply plugin: 'com.google.gms.google-services'
                                                                        I had the same problem or similar,
Make sure that in your google-services.json you have:
...    
"client": [
        ...
          "oauth_client": [
            ...
            {
              "client_id": "YOUR WEB CLIENT ID",
              "client_type": 3
            }     
...
For some reason the file downloaded from firebase console doesn't include it.
After adding the entry in the google-services.json file, everything started working as expected.
google-services-plugin documentation
Try downloading your .json file again after changing the configuration in the Firebase console. Use this newer configuration file, not the old one.
For me the problem was because I was using minSdkVersion 15, updating to 16 has solved my problem.
Sometimes there is issue while parsing google-services.json. I have reported this issue with to concerned team.
Meanwhile follow below step to fix this issue to get going further -
1) Open google-services.json file -> client -> oauth_client -> client_id
2) Copy this client ID and hardcode this .requestIdToken("your ID")
It would allow to request "IdToken" via GoogleSignInAccount post successful google login and to authorize your credential with firebase.
EDIT
Try deleting and recreating the project and re-importing new google-service.jsonin your Android project
After a time searching the "smart" fix without insert directly the client_id, following this answer from FirebaseUI project I just need to add the next line in app/build.gradle:
implementation 'com.firebaseui:firebase-ui-auth:4.3.2'