YAML Configuration Interpolation#

Tinyauth's YAML loader intentionally does not resolve ${...} environment variable references inside YAML configuration files. If you write secret: ${MY_SECRET} in a config file, the literal string "${MY_SECRET}" will be stored in the config field — no substitution occurs.

This is a deliberate design boundary: YAML files and environment variables are fully separate configuration sources that never cross-interpolate.

How the Loader Works#

The YAML (and TOML/JSON) loading path in paerser is a pure parse-and-map pipeline:

1. File read → raw map – decodeFileToNode reads the file with yaml.Unmarshal directly into a map[string]interface{}. No string pre-processing happens before or after this step.
2. Raw map → node tree – decodeRawToNode walks the map and copies string values verbatim into parser.Node structs via getSimpleValue, which performs only type coercion (int, bool, float → string) — not template expansion.
3. Node tree → typed struct – parser.Fill maps node values onto the Config struct fields.

There is no step in this pipeline that scans values for ${...} patterns or calls os.Getenv 1.

In Tinyauth itself, FileLoader.Load resolves the config file path from either the --traefik.configfile flag or TINYAUTH_CONFIGFILE env var, then hands off to file.Decode() — again with no interpolation of the file's contents.

Why This Matters#

Tinyauth runs three loaders in sequence at startup 2:

FileLoader → FlagLoader → EnvLoader

EnvLoader runs last and therefore has the highest priority, overriding values from YAML. This layered override model is the intended way to inject runtime secrets or environment-specific values: set them as environment variables (e.g., TINYAUTH_SERVER_SECRET), not as ${...} references inside YAML.

Practical consequence: Do not use shell-style variable interpolation in Tinyauth YAML files. Secrets and per-environment overrides belong in environment variables, which are loaded independently by EnvLoader via paerser/env.

Key Source Files#

For the full configuration source model (priority order, env var naming conventions, available options), see the Configuration Sources knowledge base article.