package middleware import ( "context" "fmt" "net/http" "net/url" "github.com/superseriousbusiness/gotosocial/internal/ap" "github.com/superseriousbusiness/gotosocial/internal/db" "github.com/superseriousbusiness/gotosocial/internal/log" "github.com/gin-gonic/gin" "github.com/go-fed/httpsig" ) var ( // this mimics an untyped error returned by httpsig when no signature is present; // define it here so that we can use it to decide what to log without hitting // performance too hard noSignatureError = fmt.Sprintf("neither %q nor %q have signature parameters", httpsig.Signature, httpsig.Authorization) signatureHeader = string(httpsig.Signature) authorizationHeader = string(httpsig.Authorization) ) // SignatureCheck returns a gin middleware for checking http signatures. // // The middleware first checks whether an incoming http request has been http-signed with a well-formed signature. // // If so, it will check if the domain that signed the request is permitted to access the server, using the provided isURIBlocked function. // // If it is permitted, the handler will set the key verifier and the signature in the gin context for use down the line. // // If the domain is blocked, the middleware will abort the request chain instead with http code 403 forbidden. // // In case of an error, the request will be aborted with http code 500 internal server error. func SignatureCheck(isURIBlocked func(context.Context, *url.URL) (bool, db.Error)) func(*gin.Context) { return func(c *gin.Context) { // Acquire ctx from gin request. ctx := c.Request.Context() // create the verifier from the request, this will error if the request wasn't signed verifier, err := httpsig.NewVerifier(c.Request) if err != nil { // Something went wrong, so we need to return regardless, but only actually // *abort* the request with 401 if a signature was present but malformed if err.Error() != noSignatureError { log.Debugf(ctx, "http signature was present but invalid: %s", err) c.AbortWithStatus(http.StatusUnauthorized) } return } // The request was signed! // The key ID should be given in the signature so that we know where to fetch it from the remote server. // This will be something like https://example.org/users/whatever_requesting_user#main-key requestingPublicKeyIDString := verifier.KeyId() requestingPublicKeyID, err := url.Parse(requestingPublicKeyIDString) if err != nil { log.Debugf(ctx, "http signature requesting public key id %s could not be parsed as a url: %s", requestingPublicKeyIDString, err) c.AbortWithStatus(http.StatusUnauthorized) return } else if requestingPublicKeyID == nil { // Key can sometimes be nil, according to url parse function: // 'Trying to parse a hostname and path without a scheme is invalid but may not necessarily return an error, due to parsing ambiguities' log.Debugf(ctx, "http signature requesting public key id %s was nil after parsing as a url", requestingPublicKeyIDString) c.AbortWithStatus(http.StatusUnauthorized) return } // we managed to parse the url! // if the domain is blocked we want to bail as early as possible if blocked, err := isURIBlocked(c.Request.Context(), requestingPublicKeyID); err != nil { log.Errorf(ctx, "could not tell if domain %s was blocked or not: %s", requestingPublicKeyID.Host, err) c.AbortWithStatus(http.StatusInternalServerError) return } else if blocked { log.Infof(ctx, "domain %s is blocked", requestingPublicKeyID.Host) c.AbortWithStatus(http.StatusForbidden) return } // assume signature was set on Signature header (most common behavior), // but fall back to Authorization header if necessary var signature string if s := c.GetHeader(signatureHeader); s != "" { signature = s } else { signature = c.GetHeader(authorizationHeader) } // set the verifier and signature on the context here to save some work further down the line c.Set(string(ap.ContextRequestingPublicKeyVerifier), verifier) c.Set(string(ap.ContextRequestingPublicKeySignature), signature) } }