Code snippets of Token refresh implementation with Ktor in Kotlin Multiplatform Mobile - Medium Post - https://medium.com/@lahirujay

AndroidModule.kt

actual fun platformNetModule(): Module = module {
    single {
        OkHttp.create {
            preconfigured = getOkHttpClient()
        }
    }
}

fun getOkHttpClient(): OkHttpClient {
    return OkHttpClient.Builder()
        .build()
}

build.gradle.kts

val commonMain by getting {
    dependencies {
        implementation("io.ktor:ktor-client-core:$ktorVersion")
        implementation("io.ktor:ktor-client-content-negotiation:$ktorVersion")
        implementation("io.ktor:ktor-client-logging:$ktorVersion")
        implementation("io.ktor:ktor-client-auth:$ktorVersion")
        implementation("io.ktor:ktor-serialization-kotlinx-json:$ktorVersion")
        implementation("io.insert-koin:koin-core:$koinVersion")
        implementation("io.github.aakira:napier:$napierVersion")
    }
}   

val androidMain by getting {
    dependencies {
        implementation("io.ktor:ktor-client-okhttp:$ktorVersion")
    }
}

val iosMain by creating {
    dependsOn(commonMain)
    iosX64Main.dependsOn(this)
    iosArm64Main.dependsOn(this)
    iosSimulatorArm64Main.dependsOn(this)
    dependencies {
        implementation("io.ktor:ktor-client-darwin:$ktorVersion")
    }
}

IosModule.kt

actual fun platformNetModule(): Module = module {
    single { Darwin.create() }
}

koin.kt

fun initKoin(
    enableLogs: Boolean = false,
    baseUrl: String, clientId: String, appDeclaration: KoinAppDeclaration = {}
) = startKoin {
    appDeclaration()
    modules(
        
        platformNetModule(),
        
        networkModule(enableLogs, baseUrl, clientId),
        userManagerModule(),
        //...
    )
}

//IOS
fun KoinApplication.Companion.start(baseUrl: String,clientId: String): KoinApplication =
    initKoin(enableLogs = true, baseUrl = baseUrl, clientId = clientId) { }

NetworkModule-1.kt

expect fun platformNetModule(): Module

NetworkModule-2.kt

fun networkModule(enableLogs: Boolean, baseUrl: String, clientId: String) = module {
    single {
        HttpClient(get()) {
            expectSuccess = true
            install(Auth){
                bearer {
                    loadTokens {
                        val userManager: UserManager = get() // Secure Token Store
                        val accessToken = userManager.get().accessToken
                        val refreshToken = userManager.get().refreshToken

                        BearerTokens(accessToken!!,refreshToken!!)
                    }

                    refreshTokens {
                        val userManager: UserManager = get() // Secure Token Store
                        
                        val refreshTokenInfo: TokenInfo = client.submitForm(
                            url = "token",
                            formParameters = Parameters.build {
                                append("grant_type", "refresh_token")
                                append("client_id", clientId)
                                append("refresh_token", userManager.get().refreshToken ?: "")
                            }
                        ) { markAsRefreshTokenRequest() }.body()

                        userManager.connect(
                            SessionData(
                                accessToken = refreshTokenInfo
                                    .accessToken,
                                idToken = refreshTokenInfo.idToken,
                                refreshToken = refreshTokenInfo.refreshToken
                            )
                        )

                        val accessToken = refreshTokenInfo.accessToken
                        val refreshToken = userManager.get().refreshToken

                        BearerTokens(accessToken, refreshToken!!)
                    }
                }
            }

            defaultRequest {
                url {
                    host = baseUrl
                    url { protocol = URLProtocol.HTTPS }
                }
            }

            install(Logging) {
                logger = object : Logger {
                    override fun log(message: String) {
                        Napier.v(message = message, tag = "HTTPS Client")
                    }
                }
                level = LogLevel.ALL
            }

            install(ContentNegotiation) {
                json(Json {
                    prettyPrint = true
                    isLenient = true
                    ignoreUnknownKeys = true
                })
            }
        }
    }
}

NetworkModule-part.kt

install(Auth){
                bearer {
                    refreshTokens {
                        val refreshTokenInfo: TokenInfo = client.submitForm(
                            url = "token", //token endpoint
                            formParameters = Parameters.build {
                                append("grant_type", "refresh_token")
                                append("client_id", "YOUR_CLIENT_ID")
                                append("refresh_token", "CURRENT_REFRESH_TOKEN")
                            }
                        ) { markAsRefreshTokenRequest() }.body()

                        val accessToken = refreshTokenInfo.accessToken
                        val refreshToken = refreshTokenInfo.refreshToken
                        
                        BearerTokens(accessToken, refreshToken)
                    }
                }
            }