lcobucci/jwt · error · Lcobucci\JWT\Signer\Key\FileCouldNotBeRead

The path " " does not contain a valid key file

Error message

The path "{path}" does not contain a valid key file

What it means

Thrown by InMemory::file() when the given path cannot be opened as a key file — typically because the file does not exist or is not readable. The underlying SplFileObject/IO failure is wrapped via FileCouldNotBeRead::onPath().

Solutions

1. Verify the file exists at the exact absolute path: `ls -l /path/to/key.pem`
2. Check read permissions for the process user (`chmod 644` or fix ownership)
3. Mount the secret volume correctly (Docker/K8s) before the app starts
4. Use an absolute path instead of a relative one to avoid CWD surprises

Example fix

// before
$key = InMemory::file('keys/private.pem'); // depends on CWD
// after
$key = InMemory::file(__DIR__ . '/keys/private.pem');

if (!is_file($path) || !is_readable($path)) { throw new RuntimeException("Key file missing or unreadable: $path"); }

try { $key = InMemory::file($path); } catch (\Jose\Component\Core\Exception\FileCouldNotBeRead $e) { /* log path + prior exception; fail fast */ }

When it happens

Trigger: Calling InMemory::file('/path/to/key.pem') where the path does not exist, is a directory, or the process lacks read permission; also resolving 'file://' key references (e.g. docker secrets paths) that were not mounted.

Common situations: Docker/K8s secret file not mounted at the expected path, relative path resolved from a different working directory, wrong filename or typo, file permissions after deployment.

Understand the failure class

Background: "File not found" and ENOENT errors: why libraries can't find a file that should exist — this error's family across 50 libraries.

Related errors

• Key cannot be empty
• There was an error while creating the signature
• It was not possible to parse your key, reason

AI-assisted analysis of lcobucci/jwt@375813049c (2026-09-14). Data as JSON: /api/errors/8708a44debedfc7a. Report an issue: GitHub.

Appendix: source

Thrown at src/Signer/Key/InMemory.php:69

        self::guardAgainstEmptyKey($decoded); // @phpstan-ignore staticMethod.alreadyNarrowedType

        return new self($decoded, $passphrase);
    }

    /**
     * @param non-empty-string $path
     *
     * @throws FileCouldNotBeRead
     */
    public static function file(
        string $path,
        #[SensitiveParameter]
        string $passphrase = '',
    ): self {
        try {
            $file = new SplFileObject($path);
        } catch (Throwable $exception) {
            throw FileCouldNotBeRead::onPath($path, $exception);
        }

        $fileSize = $file->getSize();
        $contents = $fileSize > 0 ? $file->fread($file->getSize()) : '';
        assert(is_string($contents));

        self::guardAgainstEmptyKey($contents);

        return new self($contents, $passphrase);
    }

    /** @phpstan-assert non-empty-string $contents */
    private static function guardAgainstEmptyKey(string $contents): void
    {
        if ($contents === '') {
            throw InvalidKeyProvided::cannotBeEmpty();
        }
    }

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