package auth
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import (
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"context"
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"crypto/subtle"
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"fmt"
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"net/http"
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"net/url"
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"sort"
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"strconv"
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"strings"
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"sync"
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"time"
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)
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type digestClient struct {
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nc uint64
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lastSeen int64
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}
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// DigestAuth is an authenticator implementation for 'Digest' HTTP Authentication scheme (RFC 7616).
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//
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// Note: this implementation was written following now deprecated RFC
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// 2617, and supports only MD5 algorithm.
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//
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// TODO: Add support for SHA-256 and SHA-512/256 algorithms.
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type DigestAuth struct {
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Realm string
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Opaque string
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Secrets SecretProvider
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PlainTextSecrets bool
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IgnoreNonceCount bool
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// Headers used by authenticator. Set to ProxyHeaders to use with
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// proxy server. When nil, NormalHeaders are used.
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Headers *Headers
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/*
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Approximate size of Client's Cache. When actual number of
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tracked client nonces exceeds
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ClientCacheSize+ClientCacheTolerance, ClientCacheTolerance*2
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older entries are purged.
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*/
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ClientCacheSize int
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ClientCacheTolerance int
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clients map[string]*digestClient
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mutex sync.RWMutex
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}
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// check that DigestAuth implements AuthenticatorInterface
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var _ = (AuthenticatorInterface)((*DigestAuth)(nil))
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type digestCacheEntry struct {
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nonce string
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lastSeen int64
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}
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type digestCache []digestCacheEntry
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func (c digestCache) Less(i, j int) bool {
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return c[i].lastSeen < c[j].lastSeen
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}
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func (c digestCache) Len() int {
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return len(c)
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}
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func (c digestCache) Swap(i, j int) {
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c[i], c[j] = c[j], c[i]
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}
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// Purge removes count oldest entries from DigestAuth.clients
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func (da *DigestAuth) Purge(count int) {
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da.mutex.Lock()
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da.purgeLocked(count)
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da.mutex.Unlock()
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}
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func (da *DigestAuth) purgeLocked(count int) {
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entries := make([]digestCacheEntry, 0, len(da.clients))
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for nonce, client := range da.clients {
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entries = append(entries, digestCacheEntry{nonce, client.lastSeen})
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}
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cache := digestCache(entries)
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sort.Sort(cache)
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for _, client := range cache[:count] {
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delete(da.clients, client.nonce)
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}
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}
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// RequireAuth is an http.HandlerFunc which initiates the
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// authentication process (or requires reauthentication).
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func (da *DigestAuth) RequireAuth(w http.ResponseWriter, r *http.Request) {
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da.mutex.RLock()
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clientsLen := len(da.clients)
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da.mutex.RUnlock()
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if clientsLen > da.ClientCacheSize+da.ClientCacheTolerance {
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da.Purge(da.ClientCacheTolerance * 2)
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}
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nonce := RandomKey()
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da.mutex.Lock()
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da.clients[nonce] = &digestClient{nc: 0, lastSeen: time.Now().UnixNano()}
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da.mutex.Unlock()
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da.mutex.RLock()
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w.Header().Set(contentType, da.Headers.V().UnauthContentType)
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w.Header().Set(da.Headers.V().Authenticate,
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fmt.Sprintf(`Digest realm="%s", nonce="%s", opaque="%s", algorithm=MD5, qop="auth"`,
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da.Realm, nonce, da.Opaque))
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w.WriteHeader(da.Headers.V().UnauthCode)
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w.Write([]byte(da.Headers.V().UnauthResponse))
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da.mutex.RUnlock()
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}
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// DigestAuthParams parses Authorization header from the
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// http.Request. Returns a map of auth parameters or nil if the header
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// is not a valid parsable Digest auth header.
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func DigestAuthParams(authorization string) map[string]string {
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s := strings.SplitN(authorization, " ", 2)
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if len(s) != 2 || s[0] != "Digest" {
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return nil
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}
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return ParsePairs(s[1])
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}
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// CheckAuth checks whether the request contains valid authentication
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// data. Returns a pair of username, authinfo, where username is the
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// name of the authenticated user or an empty string and authinfo is
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// the contents for the optional Authentication-Info response header.
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func (da *DigestAuth) CheckAuth(r *http.Request) (username string, authinfo *string) {
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da.mutex.RLock()
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defer da.mutex.RUnlock()
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username = ""
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authinfo = nil
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auth := DigestAuthParams(r.Header.Get(da.Headers.V().Authorization))
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if auth == nil {
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return "", nil
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}
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// RFC2617 Section 3.2.1 specifies that unset value of algorithm in
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// WWW-Authenticate Response header should be treated as
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// "MD5". According to section 3.2.2 the "algorithm" value in
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// subsequent Request Authorization header must be set to whatever
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// was supplied in the WWW-Authenticate Response header. This
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// implementation always returns an algorithm in WWW-Authenticate
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// header, however there seems to be broken clients in the wild
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// which do not set the algorithm. Assume the unset algorithm in
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// Authorization header to be equal to MD5.
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if _, ok := auth["algorithm"]; !ok {
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auth["algorithm"] = "MD5"
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}
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if da.Opaque != auth["opaque"] || auth["algorithm"] != "MD5" || auth["qop"] != "auth" {
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return "", nil
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}
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// Check if the requested URI matches auth header
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if r.RequestURI != auth["uri"] {
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// We allow auth["uri"] to be a full path prefix of request-uri
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// for some reason lost in history, which is probably wrong, but
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// used to be like that for quite some time
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// (https://tools.ietf.org/html/rfc2617#section-3.2.2 explicitly
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// says that auth["uri"] is the request-uri).
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//
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// TODO: make an option to allow only strict checking.
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switch u, err := url.Parse(auth["uri"]); {
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case err != nil:
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return "", nil
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case r.URL == nil:
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return "", nil
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case len(u.Path) > len(r.URL.Path):
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return "", nil
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case !strings.HasPrefix(r.URL.Path, u.Path):
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return "", nil
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}
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}
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HA1 := da.Secrets(auth["username"], da.Realm)
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if da.PlainTextSecrets {
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HA1 = H(auth["username"] + ":" + da.Realm + ":" + HA1)
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}
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HA2 := H(r.Method + ":" + auth["uri"])
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KD := H(strings.Join([]string{HA1, auth["nonce"], auth["nc"], auth["cnonce"], auth["qop"], HA2}, ":"))
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if subtle.ConstantTimeCompare([]byte(KD), []byte(auth["response"])) != 1 {
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return "", nil
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}
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// At this point crypto checks are completed and validated.
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// Now check if the session is valid.
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nc, err := strconv.ParseUint(auth["nc"], 16, 64)
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if err != nil {
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return "", nil
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}
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client, ok := da.clients[auth["nonce"]]
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if !ok {
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return "", nil
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}
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if client.nc != 0 && client.nc >= nc && !da.IgnoreNonceCount {
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return "", nil
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}
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client.nc = nc
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client.lastSeen = time.Now().UnixNano()
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respHA2 := H(":" + auth["uri"])
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rspauth := H(strings.Join([]string{HA1, auth["nonce"], auth["nc"], auth["cnonce"], auth["qop"], respHA2}, ":"))
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info := fmt.Sprintf(`qop="auth", rspauth="%s", cnonce="%s", nc="%s"`, rspauth, auth["cnonce"], auth["nc"])
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return auth["username"], &info
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}
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// Default values for ClientCacheSize and ClientCacheTolerance for DigestAuth
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const (
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DefaultClientCacheSize = 1000
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DefaultClientCacheTolerance = 100
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)
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// Wrap returns an http.HandlerFunc wraps AuthenticatedHandlerFunc
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// with this DigestAuth authentication checks. Once the request
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// contains valid credentials, it calls wrapped
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// AuthenticatedHandlerFunc.
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//
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// Deprecated: new code should use NewContext instead.
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func (da *DigestAuth) Wrap(wrapped AuthenticatedHandlerFunc) http.HandlerFunc {
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return func(w http.ResponseWriter, r *http.Request) {
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if username, authinfo := da.CheckAuth(r); username == "" {
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da.RequireAuth(w, r)
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} else {
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ar := &AuthenticatedRequest{Request: *r, Username: username}
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if authinfo != nil {
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w.Header().Set(da.Headers.V().AuthInfo, *authinfo)
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}
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wrapped(w, ar)
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}
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}
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}
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// JustCheck returns a new http.HandlerFunc, which requires
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// DigestAuth to successfully authenticate a user before calling
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// wrapped http.HandlerFunc.
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//
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// Authenticated Username is passed as an extra
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// X-Authenticated-Username header to the wrapped HandlerFunc.
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func (da *DigestAuth) JustCheck(wrapped http.HandlerFunc) http.HandlerFunc {
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return da.Wrap(func(w http.ResponseWriter, ar *AuthenticatedRequest) {
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ar.Header.Set(AuthUsernameHeader, ar.Username)
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wrapped(w, &ar.Request)
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})
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}
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// NewContext returns a context carrying authentication information for the request.
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func (da *DigestAuth) NewContext(ctx context.Context, r *http.Request) context.Context {
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username, authinfo := da.CheckAuth(r)
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da.mutex.Lock()
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defer da.mutex.Unlock()
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info := &Info{Username: username, ResponseHeaders: make(http.Header)}
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if username != "" {
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info.Authenticated = true
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info.ResponseHeaders.Set(da.Headers.V().AuthInfo, *authinfo)
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} else {
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// return back digest WWW-Authenticate header
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if len(da.clients) > da.ClientCacheSize+da.ClientCacheTolerance {
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da.purgeLocked(da.ClientCacheTolerance * 2)
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}
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nonce := RandomKey()
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da.clients[nonce] = &digestClient{nc: 0, lastSeen: time.Now().UnixNano()}
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info.ResponseHeaders.Set(da.Headers.V().Authenticate,
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fmt.Sprintf(`Digest realm="%s", nonce="%s", opaque="%s", algorithm=MD5, qop="auth"`,
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da.Realm, nonce, da.Opaque))
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}
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return context.WithValue(ctx, infoKey, info)
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}
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// NewDigestAuthenticator generates a new DigestAuth object
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func NewDigestAuthenticator(realm string, secrets SecretProvider) *DigestAuth {
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da := &DigestAuth{
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Opaque: RandomKey(),
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Realm: realm,
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Secrets: secrets,
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PlainTextSecrets: true,
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ClientCacheSize: DefaultClientCacheSize,
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ClientCacheTolerance: DefaultClientCacheTolerance,
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clients: map[string]*digestClient{}}
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return da
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}
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