Gem::S3URISigner#fetch_s3_config

# File tmp/rubies/ruby-3.4.1/lib/rubygems/s3_uri_signer.rb, line 105
def fetch_s3_config
  return S3Config.new(uri.user, uri.password, nil, "us-east-1") if uri.user && uri.password

  s3_source = Gem.configuration[:s3_source] || Gem.configuration["s3_source"]
  host = uri.host
  raise ConfigurationError.new("no s3_source key exists in .gemrc") unless s3_source

  auth = s3_source[host] || s3_source[host.to_sym]
  raise ConfigurationError.new("no key for host #{host} in s3_source in .gemrc") unless auth

  provider = auth[:provider] || auth["provider"]
  case provider
  when "env"
    id = ENV["AWS_ACCESS_KEY_ID"]
    secret = ENV["AWS_SECRET_ACCESS_KEY"]
    security_token = ENV["AWS_SESSION_TOKEN"]
  when "instance_profile"
    credentials = ec2_metadata_credentials_json
    id = credentials["AccessKeyId"]
    secret = credentials["SecretAccessKey"]
    security_token = credentials["Token"]
  else
    id = auth[:id] || auth["id"]
    secret = auth[:secret] || auth["secret"]
    security_token = auth[:security_token] || auth["security_token"]
  end

  raise ConfigurationError.new("s3_source for #{host} missing id or secret") unless id && secret

  region = auth[:region] || auth["region"] || "us-east-1"
  S3Config.new(id, secret, security_token, region)
end