Unicode Normalization in Echo Go with Basic Auth

When an Echo Go service uses HTTP Basic Authentication and processes Unicode-based identifiers (such as usernames or account keys), the interaction between normalization and authentication logic can create security gaps. If the application normalizes credentials differently than the identity provider or database, an attacker can supply a visually identical string that bypasses access controls or maps to a different account.

For example, the username ｕｓｅｒ (fullwidth Latin characters) may normalize to user (ASCII), but if the service only normalizes after basic auth parsing, the credential comparison may fail to match the stored canonical value. This mismatch can allow an authenticated context to be assumed incorrectly, leading to Broken Access Control (BOLA/IDOR) or privilege confusion. The risk is especially relevant when APIs accept path parameters or headers derived from the normalized identity without re-validating against the canonical form stored server-side.

In an unauthenticated scan, middleBrick tests how the service behaves with crafted Unicode inputs and checks whether the authentication boundary remains consistent across normalization forms. Findings can include inconsistent normalization, missing canonicalization on the server side, or exposure of account relationships that should be isolated. These issues map to OWASP API Top 10 categories such as BOLA/IDOR and Input Validation, and may align with compliance frameworks like PCI-DSS and SOC2 where identity integrity is required.

To harden an Echo Go service using Basic Authentication, normalize credentials before comparison and ensure the normalized identity is used consistently across authentication, routing, and authorization checks. Use a canonical normalization form (NFC is common) on the parsed username and password, and compare against stored canonical values.

The following example demonstrates secure handling with the golang.org/x/text/unicode/norm package and the standard library’s net/http. It parses credentials, normalizes the username, validates against a mock user store, and ensures the normalized identity is used downstream.

import (
    "crypto/subtle"
    "net/http"
    "golang.org/x/text/unicode/norm"
    "strings"
)

var (
    // Canonical store: keys are NFC-normalized usernames
    users = map[string]string{
        "user": "correcthorsebatterystaple", // username: user
    }
    realm = "api.example.com"
)

func basicAuth(next http.HandlerFunc) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        user, pass, ok := r.BasicAuth()
        if !ok {
            http.Error(w, "authorization required", http.StatusUnauthorized)
            return
        }

        // Normalize to NFC to avoid comparison mismatches
        userN := norm.String(norm.NFC, user)
        passN := norm.String(norm.NFC, pass)

        expectedPass, exists := users[userN]
        if !exists || subtle.ConstantTimeCompare([]byte(passN), []byte(expectedPass)) != 1 {
            http.Error(w, "invalid credentials", http.StatusUnauthorized)
            return
        }

        // Propagate normalized identity in context for downstream checks
        ctx := context.WithValue(r.Context(), "canonicalUser", userN)
        next(w, r.WithContext(ctx))
    }
}

func accountHandler(w http.ResponseWriter, r *http.Request) {
    user, _ := r.Context().Value("canonicalUser").(string)
    // Use user (NFC-normalized) for safe lookup, avoiding BOLA/IDOR
    // e.g., fetch account by normalized key
    w.Write([]byte("account for " + user))
}

Additional remediation steps include normalizing any identifiers derived from authentication (such as API keys or tenant IDs) before they are used in routing or data access, and validating input against strict allowlists where possible. middleBrick can validate that these boundaries remain consistent by scanning the live endpoint with crafted Unicode credentials and inspecting whether the authentication surface remains predictable and isolated.