versitygw/iamapi/internal/iammiddleware/auth.go

// Copyright 2026 Versity Software
// This file is licensed under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package iammiddleware

import (
	"errors"
	"strconv"
	"time"

	"github.com/gofiber/fiber/v3"
	"github.com/versity/versitygw/debuglogger"
	"github.com/versity/versitygw/iamapi/iamerr"
	"github.com/versity/versitygw/iamapi/internal/iamutil"
	"github.com/versity/versitygw/iamapi/types"
	"github.com/versity/versitygw/internal/httpctx"
	"github.com/versity/versitygw/internal/sigv4auth"
)

const (
	SigningRegion  = "us-east-1"
	timeExpiration = 15 * time.Minute
)

// requiredSignedHeaders is the header-auth SignedHeaders policy for a
// permanent (root or AKIA…) credential. requiredTempSignedHeaders is the
// counterpart for a temporary (ASIA…) session credential: it additionally
// requires the session-token header be signed whenever it's present,
// matching standard AWS SDK behavior — defense in depth on top of the
// independent, access-key-bound SessionToken equality check in
// resolveSessionIdentity, so the header can't be silently dropped from the
// canonical request and left unbound to the signature.
//
// This only applies to header auth. Query-string (presigned) auth carries
// the token as a query parameter instead, which sigv4auth's presign query
// extraction already includes in the signed canonical query string
// regardless of SignedHeaders, so requiredSignedHeaders (unconditionally
// "host") is used for both root/permanent and session query-auth requests.
var (
	requiredSignedHeaders     = []string{"host"}
	requiredTempSignedHeaders = []string{"host", sigv4auth.HeaderSecurityToken}
)

// requiredHeaderAuthSignedHeaders returns the SignedHeaders policy
// checkSignature enforces for header-based auth, based on whether accessKey
// is a temporary (ASIA…) session credential.
func requiredHeaderAuthSignedHeaders(accessKey string) []string {
	if iamutil.IsTempAccessKeyID(accessKey) {
		return requiredTempSignedHeaders
	}
	return requiredSignedHeaders
}

type RootCredentials struct {
	Access string
	Secret string
}

// VerifyIAMAuth authenticates a request against service (sigv4auth.ServiceIAM
// or sigv4auth.ServiceSTS).
//
// Three kinds of credential are accepted: the configured root user, a
// long-term (AKIA…) IAM user access key, or a temporary (ASIA…) session
// minted by AssumeRoleWithWebIdentity. Whichever it is, the resolved
// identity (and, for a user/session, its policy documents) is stored via
// httpctx.ContextKeyCallerIdentity for the policy middleware and controllers
// to read back. Root bypasses the policy middleware entirely
func VerifyIAMAuth(service string, root *RootCredentials, store iamutil.IdentityStore) fiber.Handler {
	return func(ctx fiber.Ctx) error {
		authData, tdate, queryAuth, err := parseIAMAuth(ctx, service)
		if err != nil {
			return err
		}

		// A security token paired with root or any long-term (AKIA…)
		// credential is rejected inside sigv4auth.ParseQueryAuthorization
		// for query auth, and just below for header auth — before any
		// signature work either way, rather than letting it fall through to
		// a signature-mismatch error once a tampered/unsigned token
		// invalidates the canonical request.
		if !queryAuth && !sigv4auth.IsTempAccessKeyID(authData.Access) &&
			ctx.Get(sigv4auth.HeaderSecurityToken) != "" {
			return iamerr.GetAPIError(iamerr.ErrInvalidClientTokenID)
		}

		if authData.Access == root.Access {
			if err := checkSignature(ctx, authData, root.Secret, tdate, queryAuth, service); err != nil {
				return err
			}
			httpctx.ContextKeyCallerIdentity.Set(ctx, types.Identity{IsRoot: true})
			return nil
		}

		identity, secret, err := resolveIdentity(ctx, store, authData, queryAuth)
		if err != nil {
			return err
		}

		if err := checkSignature(ctx, authData, secret, tdate, queryAuth, service); err != nil {
			return err
		}
		httpctx.ContextKeyCallerIdentity.Set(ctx, *identity)

		// Best-effort update of a permanent access key's GetAccessKeyLastUsed
		// metadata, matching real IAM's behavior. A failure is only logged,
		// never returned: this is purely informational, and a lost update
		// under concurrent use is immaterial. Called synchronously: a Storer
		// implementation for which this is network-bound (e.g. Vault) is
		// expected to make it non-blocking itself.
		if identity.User != nil {
			if err := store.RecordAccessKeyUsage(ctx.Context(), authData.Access, service, SigningRegion, time.Now().UTC()); err != nil {
				debuglogger.Logf("failed to record access key last-used metadata for %q: %v", authData.Access, err)
			}
		}
		return nil
	}
}

// VerifyRootOnlySigV4 authenticates a request as strictly the configured
// root credential — used by the standalone IAM service's private
// endpoints, which only the S3 gateway itself ever calls, signing as its
// own configured IAM-client identity (root, or a dedicated IAM-access
// credential that defaults to root). Unlike VerifyIAMAuth, any
// other access key — valid IAM user, session, or unknown — is rejected
// outright before any signature work: there is no identity to resolve on
// behalf of here, and these two endpoints exist specifically so no identity
// other than the gateway's own ever needs to reach them.
func VerifyRootOnlySigV4(service string, root *RootCredentials) fiber.Handler {
	return func(ctx fiber.Ctx) error {
		authData, tdate, queryAuth, err := parseIAMAuth(ctx, service)
		if err != nil {
			return err
		}

		if authData.Access != root.Access {
			return iamerr.GetAPIError(iamerr.ErrInvalidClientTokenID)
		}

		return checkSignature(ctx, authData, root.Secret, tdate, queryAuth, service)
	}
}

// resolveIdentity resolves authData.Access to a session or long-term user,
// by its AKIA…/ASIA… prefix, and returns the generic identity the rest of
// the request pipeline uses along with the secret VerifyIAMAuth checks the
// signature against. It does not itself verify the SigV4 signature — the
// caller does that next, so a stolen/guessed access key or session token
// alone is never sufficient.
//
// A temporary session can be used via query-string (presigned URL)
// authentication — real AWS accepts X-Amz-Security-Token as a query
// parameter for exactly this. VerifyIAMAuth already rejects a security
// token paired with any non-temporary credential (root included) before
// this is ever reached.
func resolveIdentity(ctx fiber.Ctx, store iamutil.IdentityStore, authData sigv4auth.AuthData, queryAuth bool) (*types.Identity, string, error) {
	if store == nil {
		return nil, "", iamerr.GetAPIError(iamerr.ErrInvalidClientTokenID)
	}

	if iamutil.IsTempAccessKeyID(authData.Access) {
		return resolveSessionIdentity(ctx, store, authData, queryAuth)
	}

	identity, secret, err := iamutil.ResolveUserIdentity(ctx, store, authData.Access)
	if err != nil {
		return nil, "", iamerr.GetAPIError(iamerr.ErrInvalidClientTokenID)
	}
	return identity, secret, nil
}

// resolveSessionIdentity extracts the security token from wherever this
// request carries it and delegates to iamutil.ResolveSessionByToken, mapping
// its sentinel errors onto the control plane's single public-facing error —
// which deliberately does not distinguish "no such session" from "wrong
// token" for an unauthenticated caller.
func resolveSessionIdentity(ctx fiber.Ctx, store iamutil.IdentityStore, authData sigv4auth.AuthData, queryAuth bool) (*types.Identity, string, error) {
	token := ctx.Get(sigv4auth.HeaderSecurityToken)
	if queryAuth {
		token = ctx.Query(sigv4auth.QuerySecurityToken)
	}

	identity, secret, err := iamutil.ResolveSessionByToken(ctx.Context(), store, authData.Access, token)
	if err != nil {
		return nil, "", iamerr.GetAPIError(iamerr.ErrInvalidClientTokenID)
	}
	return identity, secret, nil
}

func checkSignature(ctx fiber.Ctx, authData sigv4auth.AuthData, secret string, tdate time.Time, queryAuth bool, service string) error {
	contentLength, err := parseContentLength(ctx.Get("Content-Length"))
	if err != nil {
		return err
	}

	derivedKey := sigv4auth.DeriveKey(secret, tdate.Format(sigv4auth.YYYYMMDD), authData.Region, service)

	payloadHash := sigv4auth.PayloadSHA256Hex(ctx.BodyRaw())
	if queryAuth {
		_, err = sigv4auth.CheckQuerySignature(ctx, authData, derivedKey, payloadHash, tdate, contentLength, sigv4auth.CheckOptions{
			Service:               service,
			RequiredSignedHeaders: requiredSignedHeaders,
		})
	} else {
		_, err = sigv4auth.CheckSignature(ctx, authData, derivedKey, payloadHash, tdate, contentLength, sigv4auth.CheckOptions{
			Service:               service,
			RequiredSignedHeaders: requiredHeaderAuthSignedHeaders(authData.Access),
		})
	}
	if err != nil {
		return mapIAMSigV4Error(err, service)
	}
	return nil
}

func parseIAMAuth(ctx fiber.Ctx, expectedService string) (sigv4auth.AuthData, time.Time, bool, error) {
	if sigv4auth.IsQueryAuth(ctx) {
		return parseIAMQueryAuth(ctx, expectedService)
	}
	if sigv4auth.IsQueryAuthV2(ctx) {
		return sigv4auth.AuthData{}, time.Time{}, false, iamerr.GetAPIError(iamerr.ErrUnsupportedSignatureVersion)
	}

	return parseIAMHeaderAuth(ctx, expectedService)
}

func parseIAMHeaderAuth(ctx fiber.Ctx, expectedService string) (sigv4auth.AuthData, time.Time, bool, error) {
	authData := sigv4auth.AuthData{}

	authorization := ctx.Get("Authorization")
	if authorization == "" {
		return authData, time.Time{}, false, iamerr.GetAPIError(iamerr.ErrMissingAuthenticationToken)
	}

	date := ctx.Get("X-Amz-Date")
	if date == "" {
		date = ctx.Get("Date")
	}
	if date == "" {
		return authData, time.Time{}, false, iamerr.IncompleteSignatureMissingDate(authorization)
	}

	tdate, err := time.Parse(sigv4auth.ISO8601Format, date)
	if err != nil {
		return authData, time.Time{}, false, iamerr.IncompleteSignatureInvalidXAmzDate(date)
	}
	if err := ValidateDateAt(tdate, time.Now().UTC()); err != nil {
		return authData, time.Time{}, false, err
	}

	authData, err = sigv4auth.ParseAuthorization(authorization, expectedService)
	if err != nil {
		return authData, time.Time{}, false, mapIAMSigV4Error(err, expectedService, authorization)
	}

	if authData.Region != SigningRegion {
		return authData, time.Time{}, false, iamerr.GetAPIError(iamerr.ErrInvalidRegion)
	}
	if date[:8] != authData.Date {
		return authData, time.Time{}, false, iamerr.GetAPIError(iamerr.ErrInvalidCredentialDate)
	}

	return authData, tdate, false, nil
}

// parseIAMQueryAuth parses SigV4 query-string (presigned URL) authentication
// parameters. Unlike S3, IAM/STS query-auth does not use X-Amz-Expires at
// all: a presigned request with X-Amz-Expires omitted, non-numeric,
// negative, or far beyond S3's 604800-second maximum is accepted every
// time, while a request merely signed too long ago is rejected with
// SignatureDoesNotMatch ("Signature expired: ... is now earlier than ...
// (... - 15 min.)") — byte-for-byte the same message this codebase's own
// SignatureDoesNotMatchExpired already produces. So X-Amz-Expires is
// neither required nor validated here, and the same fixed ±timeExpiration
// freshness window header auth uses applies to query auth too.
func parseIAMQueryAuth(ctx fiber.Ctx, expectedService string) (sigv4auth.AuthData, time.Time, bool, error) {
	authData, details, err := sigv4auth.ParseQueryAuthorization(ctx, sigv4auth.QueryAuthOptions{
		Service: expectedService,
		Region:  SigningRegion,
	})
	if err != nil {
		return authData, time.Time{}, true, mapIAMSigV4Error(err, expectedService)
	}
	if err := ValidateDateAt(details.SigningTime, time.Now().UTC()); err != nil {
		return authData, time.Time{}, true, err
	}

	return authData, details.SigningTime, true, nil
}

func parseContentLength(contentLengthStr string) (int64, error) {
	if contentLengthStr == "" {
		return 0, nil
	}

	contentLength, err := strconv.ParseInt(contentLengthStr, 10, 64)
	if err != nil {
		return 0, iamerr.GetAPIError(iamerr.ErrInvalidContentLength)
	}

	return contentLength, nil
}

// ValidateDateAt checks that date is within the allowed window relative to now.
// Exported so tests can exercise it directly.
func ValidateDateAt(date, now time.Time) error {
	if date.After(now.Add(timeExpiration)) {
		return iamerr.SignatureDoesNotMatchNotYetCurrent(date, now, timeExpiration)
	}
	if date.Before(now.Add(-timeExpiration)) {
		return iamerr.SignatureDoesNotMatchExpired(date, now, timeExpiration)
	}
	return nil
}

func mapIAMSigV4Error(err error, expectedService string, authorization ...string) error {
	var queryErr *sigv4auth.QueryError
	if errors.As(err, &queryErr) {
		return mapIAMQueryError(queryErr)
	}

	var parseErr *sigv4auth.ParseError
	if errors.As(err, &parseErr) {
		authHeader := ""
		if len(authorization) > 0 {
			authHeader = authorization[0]
		}
		return mapIAMParseError(parseErr, expectedService, authHeader)
	}

	var headersErr *sigv4auth.HeadersNotSignedError
	if errors.As(err, &headersErr) {
		if len(headersErr.Headers) == 1 && headersErr.Headers[0] == "host" {
			return iamerr.GetAPIError(iamerr.ErrMissingHostSignedHeader)
		}
		return iamerr.IncompleteSignatureHeadersNotSigned(headersErr.Headers)
	}

	var sigErr *sigv4auth.SignatureMismatchError
	if errors.As(err, &sigErr) {
		return iamerr.GetAPIError(iamerr.ErrSignatureDoesNotMatch)
	}

	return err
}

func mapIAMQueryError(err *sigv4auth.QueryError) error {
	switch err.Kind {
	case sigv4auth.ErrQueryMissingRequiredParams:
		switch err.Value {
		case sigv4auth.QueryAlgorithm:
			return iamerr.GetAPIError(iamerr.ErrMissingAuthenticationToken)
		case sigv4auth.QueryCredential, sigv4auth.QueryDate, sigv4auth.QuerySignedHeaders, sigv4auth.QuerySignature:
			return iamerr.IncompleteSignatureMissingQueryParameter(err.Value)
		default:
			return iamerr.GetAPIError(iamerr.ErrIncompleteSignature)
		}
	case sigv4auth.ErrQueryUnsupportedAlgorithm, sigv4auth.ErrQueryUnsupportedECDSA:
		return iamerr.GetAPIError(iamerr.ErrUnsupportedQueryAlgorithm)
	case sigv4auth.ErrQueryInvalidDateFormat:
		return iamerr.IncompleteSignatureInvalidXAmzDate(err.Value)
	case sigv4auth.ErrQueryDateMismatch:
		return iamerr.GetAPIError(iamerr.ErrInvalidCredentialDate)
	case sigv4auth.ErrQueryIncorrectRegion:
		return iamerr.GetAPIError(iamerr.ErrInvalidRegion)
	case sigv4auth.ErrQuerySecurityToken:
		return iamerr.GetAPIError(iamerr.ErrInvalidClientTokenID)
	default:
		return iamerr.GetAPIError(iamerr.ErrIncompleteSignature)
	}
}

func mapIAMParseError(err *sigv4auth.ParseError, expectedService, authorization string) error {
	if authorization == "" {
		authorization = err.Input
	}

	switch err.Kind {
	case sigv4auth.ErrInvalidAuthorizationHeader:
		return iamerr.GetAPIError(iamerr.ErrMissingAuthenticationToken)
	case sigv4auth.ErrUnsupportedAuthorizationVersion:
		return iamerr.GetAPIError(iamerr.ErrUnsupportedSignatureVersion)
	case sigv4auth.ErrInvalidAuthorizationType:
		return iamerr.GetAPIError(iamerr.ErrMissingAuthenticationToken)
	case sigv4auth.ErrMissingComponents:
		return iamerr.GetAPIError(iamerr.ErrMissingAuthorizationComponents)
	case sigv4auth.ErrMissingCredential:
		return iamerr.IncompleteSignatureMissingAuthorizationComponent("Credential", authorization)
	case sigv4auth.ErrMissingSignedHeaders:
		return iamerr.IncompleteSignatureMissingAuthorizationComponent("SignedHeaders", authorization)
	case sigv4auth.ErrMissingSignature:
		return iamerr.IncompleteSignatureMissingAuthorizationComponent("Signature", authorization)
	case sigv4auth.ErrMalformedComponent:
		return iamerr.IncompleteSignatureMalformedComponent(err.Value)
	case sigv4auth.ErrMalformedCredential:
		return iamerr.IncompleteSignatureMalformedCredential(err.Input)
	case sigv4auth.ErrIncorrectService:
		return iamerr.IncorrectServiceScope(expectedService)
	case sigv4auth.ErrIncorrectTerminal:
		return iamerr.GetAPIError(iamerr.ErrInvalidTerminal)
	case sigv4auth.ErrInvalidDateFormat:
		return iamerr.GetAPIError(iamerr.ErrInvalidCredentialDate)
	default:
		return iamerr.GetAPIError(iamerr.ErrIncompleteSignature)
	}
}