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Add basic signature validation as needed for LTI.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,165 @@ | ||
| package oauth1 | ||
|
|
||
| import ( | ||
| "context" | ||
| "fmt" | ||
| "net/http" | ||
| "net/url" | ||
| "regexp" | ||
| "strconv" | ||
| "strings" | ||
| ) | ||
|
|
||
| type providerRequest struct { | ||
| req *http.Request | ||
| oauthParams map[string]string | ||
| signatureToVerify string | ||
| signatureMethod string | ||
| timestamp int64 | ||
| clientKey string | ||
| nonce string | ||
| } | ||
|
|
||
| // ClientStorage represents an OAuth 1 provider's database of clients. | ||
| type ClientStorage = interface { | ||
| // GetSigner returns the signer that should be used to validate the signature for a client. | ||
| // To avoid timing attacks, GetSigner should return a Signer and a non-nil error | ||
| // if the clientKey is invalid. ValidateRequest will still compute a signature | ||
| // so that the runtime of ValidateRequest is about the same regardless of the clientKey's validity. | ||
| // The http request is also available for additional validation, e.g. checking for HTTPS. | ||
| GetSigner(ctx context.Context, clientKey, signatureMethod string, req *http.Request) (Signer, error) | ||
|
|
||
| // ValidateNonce returns an error if a nonce has been used before. | ||
| // | ||
| // Per Section 3.3 of the spec: | ||
| // The timestamp value MUST be a positive integer. Unless otherwise | ||
| // specified by the server's documentation, the timestamp is expressed | ||
| // in the number of seconds since January 1, 1970 00:00:00 GMT. | ||
| // | ||
| // A nonce is a random string, uniquely generated by the client to allow | ||
| // the server to verify that a request has never been made before and | ||
| // helps prevent replay attacks when requests are made over a non-secure | ||
| // channel. The nonce value MUST be unique across all requests with the | ||
| // same timestamp, client credentials, and token combinations. | ||
| // | ||
| // To avoid the need to retain an infinite number of nonce values for | ||
| // future checks, servers MAY choose to restrict the time period after | ||
| // which a request with an old timestamp is rejected. Note that this | ||
| // restriction implies a level of synchronization between the client's | ||
| // and server's clocks. | ||
| ValidateNonce(ctx context.Context, clientKey, nonce string, timestamp int64, req *http.Request) error | ||
| } | ||
|
|
||
| var authorizationHeaderParamPattern = regexp.MustCompile(`^\s*([^=]+)="?(\S*?)"?\s*$`) | ||
|
|
||
| func newProviderRequest(req *http.Request) (*providerRequest, error) { | ||
| authParams := make(map[string]string) | ||
| authHeader := req.Header.Get(authorizationHeaderParam) | ||
| if len(authHeader) > len(authorizationPrefix) { | ||
| authHeaderPrefix := strings.ToLower(authHeader[:len(authorizationPrefix)]) | ||
| if authHeaderPrefix == strings.ToLower(authorizationPrefix) { | ||
| authHeaderSuffix := authHeader[len(authorizationPrefix):] | ||
| for _, pair := range strings.Split(authHeaderSuffix, ",") { | ||
| if match := authorizationHeaderParamPattern.FindStringSubmatch(pair); match == nil { | ||
| return nil, fmt.Errorf("Invalid Authorization header") | ||
| } else if value, err := url.PathUnescape(match[2]); err == nil { | ||
| authParams[match[1]] = value | ||
| } else { | ||
| return nil, err | ||
| } | ||
| } | ||
| } | ||
| } | ||
| allParams, err := collectParameters(req, authParams) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| if err = checkMandatoryParams(allParams); err != nil { | ||
| return nil, err | ||
| } | ||
| sig := allParams[oauthSignatureParam] | ||
| delete(allParams, oauthSignatureParam) | ||
| timestamp, err := strconv.ParseInt(allParams[oauthTimestampParam], 10, 64) | ||
| if err != nil { | ||
| return nil, fmt.Errorf("unable to parse timestamp: %v", err) | ||
| } else if timestamp <= 0 { | ||
| return nil, fmt.Errorf("invalid timestamp %v", timestamp) | ||
| } | ||
| if version, ok := allParams[oauthVersionParam]; ok && version != defaultOauthVersion { | ||
| return nil, fmt.Errorf("incorrect oauth version %v", version) | ||
| } | ||
| preq := &providerRequest{ | ||
| req: req, | ||
| oauthParams: allParams, | ||
| signatureToVerify: sig, | ||
| signatureMethod: allParams[oauthSignatureMethodParam], | ||
| timestamp: timestamp, | ||
| clientKey: allParams[oauthConsumerKeyParam], | ||
| nonce: allParams[oauthNonceParam], | ||
| } | ||
| return preq, nil | ||
| } | ||
|
|
||
| func checkMandatoryParams(params map[string]string) error { | ||
| var missingParams []string | ||
| for _, param := range []string{oauthSignatureParam, oauthConsumerKeyParam, oauthNonceParam, oauthTimestampParam, oauthSignatureMethodParam} { | ||
| if _, ok := params[param]; !ok { | ||
| missingParams = append(missingParams, param) | ||
| } | ||
| } | ||
| if len(missingParams) > 0 { | ||
| return fmt.Errorf("missing required oauth params %v", strings.Join(missingParams, ", ")) | ||
| } | ||
| if _, hasAccessToken := params[oauthTokenParam]; hasAccessToken { | ||
| return fmt.Errorf("token signature validation not implemented") | ||
| } | ||
| return nil | ||
| } | ||
|
|
||
| var errSignatureMismatch = fmt.Errorf("signature mismatch") | ||
|
|
||
| func (r providerRequest) checkSignature(signer Signer) error { | ||
| if signer == nil { | ||
| return errSignatureMismatch | ||
| } | ||
| base := signatureBase(r.req, r.oauthParams) | ||
| signature, err := signer.Sign("", base) | ||
| if err != nil { | ||
| return err | ||
| } | ||
|
|
||
| // near constant time string comparison to avoid timing attacks | ||
| // https://rdist.root.org/2010/01/07/timing-independent-array-comparison/ | ||
| sigToVerify := r.signatureToVerify | ||
| if len(sigToVerify) != len(signature) { | ||
| return errSignatureMismatch | ||
| } | ||
| result := byte(0) | ||
| for i, r := range []byte(signature) { | ||
| result |= r ^ sigToVerify[i] | ||
| } | ||
| if result != 0 { | ||
| return errSignatureMismatch | ||
| } | ||
| return nil | ||
| } | ||
|
|
||
| // ValidateSignature checks that req contains a valid OAUTH 1 signature. | ||
| // It returns nil if the signature is valid, or an error if the validation fails. | ||
| func ValidateSignature(ctx context.Context, req *http.Request, v ClientStorage) error { | ||
| preq, err := newProviderRequest(req) | ||
| if err != nil { | ||
| return err | ||
| } | ||
| if err = v.ValidateNonce(ctx, preq.clientKey, preq.nonce, preq.timestamp, req); err != nil { | ||
| return err | ||
| } | ||
| signer, invalidClient := v.GetSigner(ctx, preq.clientKey, preq.signatureMethod, req) | ||
|
|
||
| // Check signature even if client is invalid to prevent timing attacks. | ||
| invalidSignature := preq.checkSignature(signer) | ||
| if invalidClient != nil { | ||
| return invalidClient | ||
| } | ||
| return invalidSignature | ||
| } |
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