gotosocial/internal/middleware/signaturecheck.go

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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)
}
}