Api Key Exposure in Fiber with Openid Connect

When an API built with Fiber exposes an API key and also integrates OpenID Connect (OIDC) for authentication, the combination can inadvertently amplify exposure and confusion in authorization handling. API keys are typically bearer tokens meant for service-to-service identification, while OIDC provides identity-based flows using ID tokens and access tokens issued by an authorization server. If both mechanisms are used without clear boundary rules, a developer might mistakenly treat an API key as an OIDC credential or rely on OIDC middleware to validate keys that are not JWTs.

In a Fiber app, this can manifest when route handlers or middleware assume an incoming Authorization header is an OIDC access token and attempt to validate its structure or claims, while the header actually contains a static API key. Because API keys are often long-lived and stored in configuration or environment files, they may be inadvertently logged, echoed in error messages, or passed through to downstream services that expect OIDC tokens. If the OIDC configuration (such as issuer, client ID, or JWKS URL) is misaligned with the API key’s format, the app might incorrectly bypass intended authorization checks or expose sensitive context in logs.

Attack surfaces expand when unauthenticated or improperly authenticated endpoints accept keys as query parameters or headers without enforcing strict content-type or audience validation. For example, a handler that reads req.Get("Authorization") and conditionally applies OIDC verification can be tricked into skipping checks if the key is passed in an unexpected format. Additionally, if introspection or token validation endpoints are exposed without rate limiting or input sanitization, an attacker could probe the OIDC configuration to infer issuer details or harvest metadata useful for crafting phishing or token replay attacks.

Data exposure risks also emerge when diagnostic routes or debug pages reveal environment variables containing API keys or OIDC client secrets. Because Fiber is a fast, minimalist framework, developers may omit defensive middleware in early prototypes and inadvertently ship endpoints that return stack traces or headers containing sensitive tokens. Cross-referencing OpenAPI specs with runtime findings is essential: a key expected to be an opaque string might be described as a bearer format in the spec, while runtime probes detect JWT-like patterns, indicating inconsistent handling that could confuse automated scanners and human reviewers alike.

middleBrick’s unauthenticated scan can surface these inconsistencies by testing authentication schemes, inspecting how the API responds to malformed or missing credentials, and flagging endpoints that mix identity and service tokens without clear separation. By running checks such as Authentication, Data Exposure, and Unsafe Consumption in parallel, the scanner can highlight whether API keys are transmitted in insecure contexts, whether OIDC routes lack proper audience or issuer validation, and whether responses leak tokens or configuration details.

Remediation centers on strict separation of concerns: API keys should be validated as opaque credentials via secure storage and header checks, while OIDC tokens should be validated using a dedicated OIDC middleware that enforces issuer, audience, and scope requirements. Never use the same header to convey both a key and an OIDC token, and avoid parsing or logging raw Authorization values in production.

Below is a correct Fiber example using OpenID Connect Connect middleware. This snippet configures OIDC with a well-known issuer and validates tokens before allowing access to a protected route.

package main

import (
    "log"
    "net/http"

    "github.com/gofiber/fiber/v2"
    "github.com/gofiber/fiber/v2/middleware/jwt"
)

func main() {
    app := fiber.New()

    // OIDC configuration via JWT middleware with issuer and expected audience.
    app.Use("/api/*", jwt.New(jwt.Config{
        SigningKeys: []jwt.SigningKey{
            {
                Algorithm: "RS256",
                Key:       []byte(`-----BEGIN PUBLIC KEY-----\nMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAu1SU1LfVLPHCozMxH2Mo\n...\n-----END PUBLIC KEY-----`),
            },
        },
        AuthScheme:  "Bearer",
        Validate: func(c *fiber.Ctx) error {
            // Validate issuer and audience explicitly.
            claims := jwt.ExtractClaims(c)
            if claims.Issuer != "https://your-identity-provider.com/" {
                return c.Status(fiber.StatusUnauthorized).SendString("invalid issuer")
            }
            if claims.Audience[0] != "your-api-audience" {
                return c.Status(fiber.StatusUnauthorized).SendString("invalid audience")
            }
            return c.Next()
        },
    }))

    app.Get("/api/protected", func(c *fiber.Ctx) error {
        return c.SendString("OK")
    })

    // Separate route for API key–based service auth, using a custom check.
    app.Get("/api/keysvc", func(c *fiber.Ctx) error {
        apiKey := c.Get("X-API-Key")
        if apiKey != "your-secure-key" {
            return c.Status(fiber.StatusForbidden).SendString("invalid key")
        }
        return c.SendString("OK")
    })

    log.Fatal(app.Listen(":3000"))
}

In this setup, OIDC-protected routes are prefixed with /api/* and validated via JWT middleware that checks issuer and audience. API key routes use a distinct header (X-API-Key) and avoid any OIDC validation logic. This prevents confusion in routing and ensures that tokens and keys are validated by separate mechanisms. The public key should be fetched from the provider’s JWKS endpoint in production rather than hard‑coded; this example uses a static key for clarity.

Additionally, ensure that your OpenAPI spec accurately distinguishes between security schemes: mark OIDC flows as oauth2 with scopes and the API key flow as apiKey in a header. This alignment helps scanners and developers reason about which credential type is expected where. middleBrick’s spec analysis can surface mismatches between declared schemes and runtime behavior, such as an endpoint that accepts a bearer token but is documented as requiring an API key.

Finally, enforce strict input validation and avoid logging raw Authorization headers. Configure logging to redact sensitive values and apply rate limiting to endpoints that accept keys or tokens to reduce brute-force or probing risks. Combine these practices with continuous monitoring to detect drift between spec definitions and runtime behavior.