URL encoded values for OTEL_EXPORTER_OTLP_HEADERS are not supported

[pyohannes]

What happened?

The Rust SDK should support URL encoded values in OTEL_EXPORTER_OTLP_HEADERS. For backward compatibility, also non-URL encoded values should be supported.

Both this settings should work:

OTEL_EXPORTER_OTLP_HEADERS="Authorization=Basic%20AAA"
OTEL_EXPORTER_OTLP_HEADERS="Authorization=Basic AAA"

Currently only non-URL encoded values are supported.

Additional context

The OTel specification requires values for OTEL_EXPORTER_OTLP_HEADERS to be formatted conforming with the W3C Baggage specification.

The W3C Baggage spec requires values to be URL encoded:

A value contains a string whose character encoding MUST be UTF-8 [Encoding]. Any characters outside of the baggage-octet range of characters MUST be percent-encoded. Characters which are not required to be percent-encoded MAY be percent-encoded.

This has been discussed in open-telemetry/opentelemetry-specification#3832, the result being that the behavior described in the OTel and W3C specification is desired and SDKs should support URL encoded values.

API Version

main branch, is likely an issue for all released versions

SDK Version

main branch, is likely an issue for all released versions

What Exporters are you seeing the problem on?

OTLP

Relevant log output

$ export OTEL_EXPORTER_OTLP_HEADERS=Authorization=Basic%20NzAxN[...]
$ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.09s
     Running `/home/johannes/Source/opentelemetry-rust/target/debug/basic-otlp`
OpenTelemetry trace error occurred. HTTP status client error (401 Unauthorized) for url (https://otlp-gateway-prod-us-east-0.grafana.net/otlp/v1/traces)
$ export OTEL_EXPORTER_OTLP_HEADERS="Authorization=Basic NzA[...]"
$ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.09s
     Running `/home/johannes/Source/opentelemetry-rust/target/debug/basic-otlp`
$