A string that is redacted when inspected.

Middleware options live in the client for as long as it exists, and every %Tesla.Env{} embeds its client, so a token given to a middleware would otherwise print wherever a client or env is inspected, including a Logger.error("request failed: #{inspect(env)}"). Wrapping the value keeps the redaction with the value itself, however the surrounding structure is inspected:

iex> secret = Tesla.SecretString.new("Bearer s3cret")
iex> inspect(secret)
"#Tesla.SecretString<redacted>"
iex> inspect([{"authorization", secret}])
~s([{"authorization", #Tesla.SecretString<redacted>}])
iex> to_string(secret)
"Bearer s3cret"

String.Chars returns the value, so middleware that builds a header by interpolation works with a wrapped value unchanged. The flip side is that "#{secret}" prints it: interpolate a secret where it goes on the request, never into a log message.

Examples

Tesla.client([
  {Tesla.Middleware.Headers, [{"authorization", Tesla.SecretString.new("Bearer #{token}")}]}
])

Tesla.client([
  {Tesla.Middleware.BearerAuth, token: Tesla.SecretString.new(token)}
])

Tesla.client([
  {Tesla.Middleware.BasicAuth, %{username: username, password: Tesla.SecretString.new(password)}}
])