TokenInterceptor.kt

class TokenInterceptor(
  private val preferencesService: PreferencesService, // shared prefs or data store
  private val retrofit: Retrofit,
) : Interceptor {

  override fun intercept(chain: Interceptor.Chain): Response = runBlocking {
    val request: Request = chain.request()

    val response = chain.proceed(request = request)
    if (!response.isSuccessful && response.code == 401) {
      response.close()

      // API service to get refresh token
      val tokenService: TokenService = retrofit.create(TokenService::class.java)

      val apiToken = when (val refreshTokenResult = tokenService.refreshToken(refreshTokenService)) {
        is Success -> refreshTokenResult.data
        is ActionResult.Error -> tokenService.generateToken()
      }

      preferencesService.setToken(token = apiToken.token)
      preferencesService.setRefreshToken(token = apiToken.refreshToken)

      val newRequest = request.newBuilder()
        .removeHeader("Authorization")
        .addHeader("Authorization", "Bearer " + apiToken.token)
        .build()

      chain.proceed(request = newRequest)
    } else {
      response
    }
  }
}