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WIP: Add initial SASL Support #21

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WIP: Add initial SASL Support #21

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2 changes: 2 additions & 0 deletions go.mod
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,8 @@ require (
github.com/spf13/cobra v1.1.3
github.com/spf13/viper v1.8.1
go.uber.org/zap v1.19.1
golang.org/x/crypto v0.0.0-20210921155107-089bfa567519
golang.org/x/text v0.3.8
k8s.io/apimachinery v0.22.2
k8s.io/client-go v0.22.2
)
26 changes: 19 additions & 7 deletions go.sum
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -419,6 +419,7 @@ github.com/yuin/goldmark v1.1.27/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9de
github.com/yuin/goldmark v1.1.32/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
github.com/yuin/goldmark v1.2.1/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
github.com/yuin/goldmark v1.3.5/go.mod h1:mwnBkeHKe2W/ZEtQ+71ViKU8L12m81fl3OWwC1Zlc8k=
github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
go.etcd.io/bbolt v1.3.2/go.mod h1:IbVyRI1SCnLcuJnV2u8VeU0CEYM7e686BmAb1XKL+uU=
go.etcd.io/etcd/api/v3 v3.5.0/go.mod h1:cbVKeC6lCfl7j/8jBhAK6aIYO9XOjdptoxU/nLQcPvs=
go.etcd.io/etcd/client/pkg/v3 v3.5.0/go.mod h1:IJHfcCEKxYu1Os13ZdwCwIUTUVGYTSAM3YSwc9/Ac1g=
Expand Down Expand Up @@ -452,8 +453,9 @@ golang.org/x/crypto v0.0.0-20190820162420-60c769a6c586/go.mod h1:yigFU9vqHzYiE8U
golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
golang.org/x/crypto v0.0.0-20201002170205-7f63de1d35b0/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
golang.org/x/crypto v0.0.0-20210220033148-5ea612d1eb83 h1:/ZScEX8SfEmUGRHs0gxpqteO5nfNW6axyZbBdw9A12g=
golang.org/x/crypto v0.0.0-20210220033148-5ea612d1eb83/go.mod h1:jdWPYTVW3xRLrWPugEBEK3UY2ZEsg3UU495nc5E+M+I=
golang.org/x/crypto v0.0.0-20210921155107-089bfa567519 h1:7I4JAnoQBe7ZtJcBaYHi5UtiO8tQHbUSXxL+pnGRANg=
golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
golang.org/x/exp v0.0.0-20190306152737-a1d7652674e8/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
golang.org/x/exp v0.0.0-20190510132918-efd6b22b2522/go.mod h1:ZjyILWgesfNpC6sMxTJOJm9Kp84zZh5NQWvqDGG3Qr8=
Expand Down Expand Up @@ -489,8 +491,9 @@ golang.org/x/mod v0.2.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
golang.org/x/mod v0.3.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
golang.org/x/mod v0.4.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
golang.org/x/mod v0.4.1/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
golang.org/x/mod v0.4.2 h1:Gz96sIWK3OalVv/I/qNygP42zyoKp3xptRVCWRFEBvo=
golang.org/x/mod v0.4.2/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4 h1:6zppjxzCulZykYSLyVDYbneBfbaBIQPYMevg0bEwv2s=
golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
golang.org/x/net v0.0.0-20180826012351-8a410e7b638d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
golang.org/x/net v0.0.0-20180906233101-161cd47e91fd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
Expand Down Expand Up @@ -532,8 +535,9 @@ golang.org/x/net v0.0.0-20210119194325-5f4716e94777/go.mod h1:m0MpNAwzfU5UDzcl9v
golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
golang.org/x/net v0.0.0-20210316092652-d523dce5a7f4/go.mod h1:RBQZq4jEuRlivfhVLdyRGr576XBO4/greRjx4P4O3yc=
golang.org/x/net v0.0.0-20210405180319-a5a99cb37ef4/go.mod h1:p54w0d4576C0XHj96bSt6lcn1PtDYWL6XObtHCRCNQM=
golang.org/x/net v0.0.0-20210520170846-37e1c6afe023 h1:ADo5wSpq2gqaCGQWzk7S5vd//0iyyLeAratkEoG5dLE=
golang.org/x/net v0.0.0-20210520170846-37e1c6afe023/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
golang.org/x/net v0.0.0-20220722155237-a158d28d115b h1:PxfKdU9lEEDYjdIzOtC4qFWgkU2rGHdKlKowJSMN9h0=
golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
golang.org/x/oauth2 v0.0.0-20190226205417-e64efc72b421/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
golang.org/x/oauth2 v0.0.0-20190604053449-0f29369cfe45/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
Expand All @@ -558,6 +562,7 @@ golang.org/x/sync v0.0.0-20200625203802-6e8e738ad208/go.mod h1:RxMgew5VJxzue5/jJ
golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sync v0.0.0-20201207232520-09787c993a3a/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sys v0.0.0-20180823144017-11551d06cbcc/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
Expand Down Expand Up @@ -609,22 +614,28 @@ golang.org/x/sys v0.0.0-20210330210617-4fbd30eecc44/go.mod h1:h1NjWce9XRLGQEsW7w
golang.org/x/sys v0.0.0-20210403161142-5e06dd20ab57/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210510120138-977fb7262007/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.0.0-20210616094352-59db8d763f22 h1:RqytpXGR1iVNX7psjB3ff8y7sNFinVFvkx1c8SjBkio=
golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.0.0-20210616094352-59db8d763f22/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f h1:v4INt8xihDGvnrfjMDVXGxw9wrfxYyCjk0KbXjhR55s=
golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/term v0.0.0-20201117132131-f5c789dd3221/go.mod h1:Nr5EML6q2oocZ2LXRh80K7BxOlk5/8JxuGnuhpl+muw=
golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
golang.org/x/term v0.0.0-20210220032956-6a3ed077a48d/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
golang.org/x/term v0.0.0-20210503060354-a79de5458b56 h1:b8jxX3zqjpqb2LklXPzKSGJhzyxCOZSz8ncv8Nv+y7w=
golang.org/x/term v0.0.0-20210503060354-a79de5458b56/go.mod h1:tfny5GFUkzUvx4ps4ajbZsCe5lw1metzhBm9T3x7oIY=
golang.org/x/term v0.0.0-20210927222741-03fcf44c2211 h1:JGgROgKl9N8DuW20oFS5gxc+lE67/N3FcwmBPMe7ArY=
golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
golang.org/x/text v0.3.1-0.20180807135948-17ff2d5776d2/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
golang.org/x/text v0.3.4/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
golang.org/x/text v0.3.5/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
golang.org/x/text v0.3.6 h1:aRYxNxv6iGQlyVaZmk6ZgYEDa+Jg18DxebPSrd6bg1M=
golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
golang.org/x/text v0.3.8 h1:nAL+RVCQ9uMn3vJZbV+MRnydTJFPf8qqY42YiA6MrqY=
golang.org/x/text v0.3.8/go.mod h1:E6s5w1FMmriuDzIBO73fBruAKo1PCIq6d2Q6DHfQ8WQ=
golang.org/x/time v0.0.0-20181108054448-85acf8d2951c/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
golang.org/x/time v0.0.0-20190308202827-9d24e82272b4/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
golang.org/x/time v0.0.0-20191024005414-555d28b269f0/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
Expand Down Expand Up @@ -682,8 +693,9 @@ golang.org/x/tools v0.0.0-20210105154028-b0ab187a4818/go.mod h1:emZCQorbCU4vsT4f
golang.org/x/tools v0.0.0-20210106214847-113979e3529a/go.mod h1:emZCQorbCU4vsT4fOWvOPXz4eW1wZW4PmDk9uLelYpA=
golang.org/x/tools v0.1.0/go.mod h1:xkSsbof2nBLbhDlRMhhhyNLN/zl3eTqcnHD5viDpcZ0=
golang.org/x/tools v0.1.2/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk=
golang.org/x/tools v0.1.5 h1:ouewzE6p+/VEB31YYnTbEJdi8pFqKp4P4n85vwo3DHA=
golang.org/x/tools v0.1.5/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk=
golang.org/x/tools v0.1.12 h1:VveCTK38A2rkS8ZqFY25HIDFscX5X9OoEhJd3quQmXU=
golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
Expand Down
221 changes: 220 additions & 1 deletion pkg/pg/frontend.go
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,13 +1,23 @@
package pg

import (
"bytes"
"crypto/hmac"
"crypto/md5"
"crypto/rand"
"crypto/sha256"
"encoding/base64"
"errors"
"fmt"
"io"
"net"
"strconv"
"sync"
"time"

"golang.org/x/crypto/pbkdf2"
"golang.org/x/text/secure/precis"

pgproto3 "github.com/jackc/pgproto3/v2"
)

Expand Down Expand Up @@ -109,6 +119,8 @@ func (b *PostgresFrontend) Close() error {

func (f *PostgresFrontend) HandleAuthenticationRequest(username, password string) error {
// TODO: max tries / exit condition?
var client *scramClient

for {
message, err := f.frontend.Receive()
if err != nil {
Expand All @@ -133,13 +145,49 @@ func (f *PostgresFrontend) HandleAuthenticationRequest(username, password string
case *pgproto3.ErrorResponse:
return &AuthFailedError{ErrMsg: msg}
case *pgproto3.AuthenticationSASL:
return fmt.Errorf("SASL auth not supported")
client, err = newScramClient(msg.AuthMechanisms, password)
if err != nil {
return err
}
response, err := createSASLInitialResponse(msg, client)
if err != nil {
return err
}
if err = f.Send(response); err != nil {
return err
}
case *pgproto3.AuthenticationSASLContinue:
err := client.recvServerFirstMessage(msg.Data)
if err != nil {
return err
}
if err = f.Send(createSASLFinalResponse(client)); err != nil {
return err
}
case *pgproto3.AuthenticationSASLFinal:
err := client.recvServerFinalMessage(msg.Data)
if err != nil {
return err
}
default:
return fmt.Errorf("unsupported auth request, or unexpected message")
}
}
}

func createSASLInitialResponse(msg *pgproto3.AuthenticationSASL, scramClient *scramClient) (*pgproto3.SASLInitialResponse, error) {
return &pgproto3.SASLInitialResponse{
AuthMechanism: "SCRAM-SHA-256",
Data: scramClient.clientFirstMessage(),
}, nil
}

func createSASLFinalResponse(scramClient *scramClient) *pgproto3.SASLResponse {
return &pgproto3.SASLResponse{
Data: []byte(scramClient.clientFinalMessage()),
}
}

func createMD5Password(username string, password string, salt string) string {
// Concatenate the password and the username together.
passwordString := fmt.Sprintf("%s%s", password, username)
Expand All @@ -163,3 +211,174 @@ func createCleartext(msg *pgproto3.AuthenticationCleartextPassword, username, pa
Password: password,
}
}

/**
*/
const clientNonceLen = 18

// From PGX
type scramClient struct {
serverAuthMechanisms []string
password []byte
clientNonce []byte

clientFirstMessageBare []byte

serverFirstMessage []byte
clientAndServerNonce []byte
salt []byte
iterations int

saltedPassword []byte
authMessage []byte
}

func newScramClient(serverAuthMechanisms []string, password string) (*scramClient, error) {
sc := &scramClient{
serverAuthMechanisms: serverAuthMechanisms,
}

// Ensure server supports SCRAM-SHA-256
hasScramSHA256 := false
for _, mech := range sc.serverAuthMechanisms {
if mech == "SCRAM-SHA-256" {
hasScramSHA256 = true
break
}
}
if !hasScramSHA256 {
return nil, errors.New("server does not support SCRAM-SHA-256")
}

// precis.OpaqueString is equivalent to SASLprep for password.
var err error
sc.password, err = precis.OpaqueString.Bytes([]byte(password))
if err != nil {
// PostgreSQL allows passwords invalid according to SCRAM / SASLprep.
sc.password = []byte(password)
}

buf := make([]byte, clientNonceLen)
_, err = rand.Read(buf)
if err != nil {
return nil, err
}
sc.clientNonce = make([]byte, base64.RawStdEncoding.EncodedLen(len(buf)))
base64.RawStdEncoding.Encode(sc.clientNonce, buf)

return sc, nil
}

func (sc *scramClient) clientFirstMessage() []byte {
sc.clientFirstMessageBare = []byte(fmt.Sprintf("n=,r=%s", sc.clientNonce))
return []byte(fmt.Sprintf("n,,%s", sc.clientFirstMessageBare))
}

func (sc *scramClient) recvServerFirstMessage(serverFirstMessage []byte) error {
sc.serverFirstMessage = serverFirstMessage
buf := serverFirstMessage
if !bytes.HasPrefix(buf, []byte("r=")) {
return errors.New("invalid SCRAM server-first-message received from server: did not include r=")
}
buf = buf[2:]

idx := bytes.IndexByte(buf, ',')
if idx == -1 {
return errors.New("invalid SCRAM server-first-message received from server: did not include s=")
}
sc.clientAndServerNonce = buf[:idx]
buf = buf[idx+1:]

if !bytes.HasPrefix(buf, []byte("s=")) {
return errors.New("invalid SCRAM server-first-message received from server: did not include s=")
}
buf = buf[2:]

idx = bytes.IndexByte(buf, ',')
if idx == -1 {
return errors.New("invalid SCRAM server-first-message received from server: did not include i=")
}
saltStr := buf[:idx]
buf = buf[idx+1:]

if !bytes.HasPrefix(buf, []byte("i=")) {
return errors.New("invalid SCRAM server-first-message received from server: did not include i=")
}
buf = buf[2:]
iterationsStr := buf

var err error
sc.salt, err = base64.StdEncoding.DecodeString(string(saltStr))
if err != nil {
return fmt.Errorf("invalid SCRAM salt received from server: %w", err)
}

sc.iterations, err = strconv.Atoi(string(iterationsStr))
if err != nil || sc.iterations <= 0 {
return fmt.Errorf("invalid SCRAM iteration count received from server: %w", err)
}

if !bytes.HasPrefix(sc.clientAndServerNonce, sc.clientNonce) {
return errors.New("invalid SCRAM nonce: did not start with client nonce")
}

if len(sc.clientAndServerNonce) <= len(sc.clientNonce) {
return errors.New("invalid SCRAM nonce: did not include server nonce")
}

return nil
}

func (sc *scramClient) clientFinalMessage() string {
clientFinalMessageWithoutProof := []byte(fmt.Sprintf("c=biws,r=%s", sc.clientAndServerNonce))

sc.saltedPassword = pbkdf2.Key([]byte(sc.password), sc.salt, sc.iterations, 32, sha256.New)
sc.authMessage = bytes.Join([][]byte{sc.clientFirstMessageBare, sc.serverFirstMessage, clientFinalMessageWithoutProof}, []byte(","))

clientProof := computeClientProof(sc.saltedPassword, sc.authMessage)

return fmt.Sprintf("%s,p=%s", clientFinalMessageWithoutProof, clientProof)
}

func (sc *scramClient) recvServerFinalMessage(serverFinalMessage []byte) error {
if !bytes.HasPrefix(serverFinalMessage, []byte("v=")) {
return errors.New("invalid SCRAM server-final-message received from server")
}

serverSignature := serverFinalMessage[2:]

if !hmac.Equal(serverSignature, computeServerSignature(sc.saltedPassword, sc.authMessage)) {
return errors.New("invalid SCRAM ServerSignature received from server")
}

return nil
}

func computeHMAC(key, msg []byte) []byte {
mac := hmac.New(sha256.New, key)
mac.Write(msg)
return mac.Sum(nil)
}

func computeClientProof(saltedPassword, authMessage []byte) []byte {
clientKey := computeHMAC(saltedPassword, []byte("Client Key"))
storedKey := sha256.Sum256(clientKey)
clientSignature := computeHMAC(storedKey[:], authMessage)

clientProof := make([]byte, len(clientSignature))
for i := 0; i < len(clientSignature); i++ {
clientProof[i] = clientKey[i] ^ clientSignature[i]
}

buf := make([]byte, base64.StdEncoding.EncodedLen(len(clientProof)))
base64.StdEncoding.Encode(buf, clientProof)
return buf
}

func computeServerSignature(saltedPassword []byte, authMessage []byte) []byte {
serverKey := computeHMAC(saltedPassword, []byte("Server Key"))
serverSignature := computeHMAC(serverKey, authMessage)
buf := make([]byte, base64.StdEncoding.EncodedLen(len(serverSignature)))
base64.StdEncoding.Encode(buf, serverSignature)
return buf
}
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