What causes "%q is not a supported encoding method" in gohugoio/hugo?

Use `hex` (default) or `binary` as the encoding argument.

is not a supported encoding method

Error message

%q is not a supported encoding method

What it means

`crypto.HMAC` accepts an optional fourth argument selecting output encoding (crypto.go:164-179). After defaulting to `hex`, it matches only `binary` or `hex`; any other value reaches the `default` arm and returns this error quoting the unsupported encoding.

Solutions

Use `hex` (default) or `binary` as the encoding argument.
For base64, take the hex output and apply `encoding.Base64Encode` on the decoded bytes, or compute in Go.
Omit the encoding argument to get hex.

Example fix

// before
{{ crypto.HMAC "sha256" $key $msg "base64" }}
// after
{{ crypto.HMAC "sha256" $key $msg "hex" }}
{{ crypto.HMAC "sha256" $key $msg }}

Defensive patterns

Strategy: validation

Validate before calling

{{/* Valid encodings: hex (default), binary */}}
{{ crypto.HMAC "sha256" $key $msg }}
{{ crypto.HMAC "sha256" $key $msg "binary" }}

Prevention

Use only `hex` or `binary` for the encoding argument.
Omit the arg entirely for hex output.
Post-process hex output for base64 in a separate step if needed.

When it happens

Trigger: `{{ crypto.HMAC "sha256" $key $msg "base64" }}` (base64 not supported), `{{ crypto.HMAC ... "HEX" }}` (uppercase), or a typo.

Common situations: Expecting base64 output (common for tokens/signatures); passing uppercase; copy-pasting an encoding name from a different library.

Related errors

AI-assisted analysis of gohugoio/hugo@52c9bd7908 (2026-08-09). Data as JSON: /api/errors/4702c18d2c77f9fc. Report an issue: GitHub.

Appendix: source

Thrown at tpl/crypto/crypto.go:178

	if err != nil {
		return "", err
	}

	encoding := "hex"
	if len(e) > 0 && e[0] != nil {
		encoding, err = cast.ToStringE(e[0])
		if err != nil {
			return "", err
		}
	}

	switch encoding {
	case "binary":
		return string(mac.Sum(nil)[:]), nil
	case "hex":
		return hex.EncodeToString(mac.Sum(nil)[:]), nil
	default:
		return "", fmt.Errorf("%q is not a supported encoding method", encoding)
	}
}

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