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101 lines
2.3 KiB
Go
101 lines
2.3 KiB
Go
package slack
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import (
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"crypto/hmac"
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"crypto/sha256"
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"encoding/hex"
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"fmt"
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"hash"
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"net/http"
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"strconv"
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"strings"
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"time"
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)
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// Signature headers
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const (
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hSignature = "X-Slack-Signature"
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hTimestamp = "X-Slack-Request-Timestamp"
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)
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// SecretsVerifier contains the information needed to verify that the request comes from Slack
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type SecretsVerifier struct {
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signature []byte
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hmac hash.Hash
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}
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func unsafeSignatureVerifier(header http.Header, secret string) (_ SecretsVerifier, err error) {
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var (
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bsignature []byte
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)
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signature := header.Get(hSignature)
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stimestamp := header.Get(hTimestamp)
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if signature == "" || stimestamp == "" {
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return SecretsVerifier{}, ErrMissingHeaders
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}
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if bsignature, err = hex.DecodeString(strings.TrimPrefix(signature, "v0=")); err != nil {
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return SecretsVerifier{}, err
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}
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hash := hmac.New(sha256.New, []byte(secret))
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if _, err = hash.Write([]byte(fmt.Sprintf("v0:%s:", stimestamp))); err != nil {
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return SecretsVerifier{}, err
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}
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return SecretsVerifier{
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signature: bsignature,
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hmac: hash,
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}, nil
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}
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// NewSecretsVerifier returns a SecretsVerifier object in exchange for an http.Header object and signing secret
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func NewSecretsVerifier(header http.Header, secret string) (sv SecretsVerifier, err error) {
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var (
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timestamp int64
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)
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stimestamp := header.Get(hTimestamp)
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if sv, err = unsafeSignatureVerifier(header, secret); err != nil {
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return SecretsVerifier{}, err
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}
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if timestamp, err = strconv.ParseInt(stimestamp, 10, 64); err != nil {
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return SecretsVerifier{}, err
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}
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diff := absDuration(time.Since(time.Unix(timestamp, 0)))
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if diff > 5*time.Minute {
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return SecretsVerifier{}, ErrExpiredTimestamp
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}
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return sv, err
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}
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func (v *SecretsVerifier) Write(body []byte) (n int, err error) {
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return v.hmac.Write(body)
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}
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// Ensure compares the signature sent from Slack with the actual computed hash to judge validity
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func (v SecretsVerifier) Ensure() error {
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computed := v.hmac.Sum(nil)
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// use hmac.Equal prevent leaking timing information.
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if hmac.Equal(computed, v.signature) {
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return nil
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}
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return fmt.Errorf("Expected signing signature: %s, but computed: %s", hex.EncodeToString(v.signature), hex.EncodeToString(computed))
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}
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func abs64(n int64) int64 {
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y := n >> 63
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return (n ^ y) - y
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}
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func absDuration(n time.Duration) time.Duration {
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return time.Duration(abs64(int64(n)))
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}
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