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validator.go
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validator.go
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// SPDX-FileCopyrightText: 2020 SAP SE or an SAP affiliate company and Cloud Security Client Go contributors
//
// SPDX-License-Identifier: Apache-2.0
package auth
import (
"errors"
"fmt"
"regexp"
"strings"
"time"
"github.com/lestrrat-go/jwx/jws"
"github.com/lestrrat-go/jwx/jwt"
"github.com/sap/cloud-security-client-go/oidcclient"
)
// parseAndValidateJWT parses the token into its claims, verifies the claims and verifies the signature
func (m *Middleware) parseAndValidateJWT(rawToken string) (Token, error) {
token, err := NewToken(rawToken)
if err != nil {
return Token{}, err
}
// get keyset
keySet, err := m.getOIDCTenant(token.Issuer(), token.CustomIssuer())
if err != nil {
return Token{}, err
}
// verify claims
if err := m.validateClaims(token, keySet); err != nil {
return Token{}, err
}
// verify signature
if err := m.verifySignature(token, keySet); err != nil {
return Token{}, err
}
return token, nil
}
func (m *Middleware) verifySignature(t Token, keySet *oidcclient.OIDCTenant) (err error) {
headers, err := getHeaders(t.TokenValue())
if err != nil {
return err
}
alg := headers.Algorithm()
// fail early to avoid another parsing of encoded token
if alg == "" {
return errors.New("alg is missing from jwt header")
}
// parse and verify signature
tenantOpts := oidcclient.ClientInfo{
ClientID: m.identity.GetClientID(),
AppTID: t.AppTID(),
Azp: t.Azp(),
}
jwks, err := keySet.GetJWKs(tenantOpts)
if err != nil {
return err
}
_, err = jwt.ParseString(t.TokenValue(), jwt.WithKeySet(jwks), jwt.UseDefaultKey(true))
if err != nil {
return err
}
return nil
}
func getHeaders(encodedToken string) (jws.Headers, error) {
msg, err := jws.Parse([]byte(encodedToken))
if err != nil {
return nil, err
}
return msg.Signatures()[0].ProtectedHeaders(), nil
}
func (m *Middleware) validateClaims(t Token, ks *oidcclient.OIDCTenant) error { // performing IsExpired check, because dgriljalva jwt.Validate() doesn't fail on missing 'exp' claim
// performing IsExpired check, because lestrrat-go jwt.Validate() doesn't fail on missing 'exp' claim
if t.IsExpired() {
return fmt.Errorf("token is expired, exp: %v", t.Expiration())
}
err := jwt.Validate(t.getJwtToken(),
jwt.WithAudience(m.identity.GetClientID()),
jwt.WithIssuer(ks.ProviderJSON.Issuer),
jwt.WithAcceptableSkew(1*time.Minute)) // to keep leeway in sync with Token.IsExpired
if err != nil {
return fmt.Errorf("claim validation failed: %v", err)
}
return nil
}
// getOIDCTenant returns an OIDC Tenant with discovered .well-known/openid-configuration.
//
// issuer is the trusted ias issuer with SAP domain of the incoming token (token.Issuer())
//
// customIssuer represents the custom issuer of the incoming token if given (token.CustomIssuer())
func (m *Middleware) getOIDCTenant(issuer, customIssuer string) (*oidcclient.OIDCTenant, error) {
issHost, err := m.verifyIssuer(issuer)
if err != nil {
return nil, err
}
tokenIssuer := customIssuer
if customIssuer == "" {
tokenIssuer = issuer
}
oidcTenant, exp, found := m.oidcTenants.GetWithExpiration(issuer)
// redo discovery if not found, cache expired, or tokenIssuer is not the same as Issuer on providerJSON (e.g. custom domain config just changed for that tenant)
if !found || time.Now().After(exp) || oidcTenant.(*oidcclient.OIDCTenant).ProviderJSON.Issuer != tokenIssuer {
newKeySet, err, _ := m.sf.Do(issuer, func() (i interface{}, err error) {
set, err := oidcclient.NewOIDCTenant(m.options.HTTPClient, issHost)
return set, err
})
if err != nil {
return nil, fmt.Errorf("token is unverifiable: unable to perform oidc discovery: %v", err)
}
oidcTenant = newKeySet.(*oidcclient.OIDCTenant)
m.oidcTenants.SetDefault(oidcTenant.(*oidcclient.OIDCTenant).ProviderJSON.Issuer, oidcTenant)
}
return oidcTenant.(*oidcclient.OIDCTenant), nil
}
func (m *Middleware) verifyIssuer(issuer string) (issuerHost string, err error) {
// issuer must be a host or https url
issuerHost = strings.TrimPrefix(issuer, "https://")
doesMatch, err := matchesDomain(issuerHost, m.identity.GetDomains())
if err != nil {
return "", fmt.Errorf("error matching domain: %v", err)
}
if !doesMatch {
return "", fmt.Errorf("token is unverifiable: unknown server (domain doesn't match)")
}
return issuerHost, nil
}
func matchesDomain(hostname string, domains []string) (bool, error) {
for _, domain := range domains {
if !strings.HasSuffix(hostname, domain) {
continue
}
// hostname matches exactly trusted domain
if hostname == domain {
return true, nil
}
isValid, regexErr := isValidSubDomain(hostname, domain)
if regexErr != nil {
return false, regexErr
}
if isValid {
return true, nil
}
}
return false, nil
}
// isValidSubDomain additionally check subdomain because "my-accounts400.ondemand.com"
// does match Suffix, but should not be allowed
// additionally it returns false if hostname contains paths like /foo or ?test=true
func isValidSubDomain(hostname, domain string) (bool, error) {
validSubdomainPattern := fmt.Sprintf("^[a-zA-Z0-9-]{1,63}\\." + regexp.QuoteMeta(domain) + "$")
return regexp.MatchString(validSubdomainPattern, hostname)
}