lib/plugins/config/config.js/Config/validate
class Config:  validate() {
    const provider = this.options.provider.toLowerCase();

    if (!validProviders.has(provider)) {
      const errorMessage = [
        `Provider "${provider}" is not supported.`,
        ` Supported providers are: ${humanReadableProvidersList}.`,
      ].join('');
      throw new this.serverless.classes.Error(errorMessage);
    }
  }