Domain block (#76)

* start work on admin domain blocking

* move stuff around + further work on domain blocks

* move + restructure processor

* prep work for deleting account

* tidy

* go fmt

* formatting

* domain blocking more work

* check domain blocks way earlier on

* progress on delete account

* delete more stuff when an account is gone

* and more...

* domain blocky block block

* get individual domain block, delete a block

internal/api/security/signaturecheck.go

@@ -0,0 +1,69 @@
+package security
+
+import (
+	"net/http"
+	"net/url"
+
+	"github.com/gin-gonic/gin"
+	"github.com/go-fed/httpsig"
+	"github.com/superseriousbusiness/gotosocial/internal/db"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/util"
+)
+
+// SignatureCheck checks whether an incoming http request has been signed. If so, it will check if the domain
+// that signed the request is permitted to access the server. If it is permitted, the handler will set the key
+// verifier in the gin context for use down the line.
+func (m *Module) SignatureCheck(c *gin.Context) {
+	l := m.log.WithField("func", "DomainBlockChecker")
+
+	// set this extra field for signature validation
+	c.Request.Header.Set("host", m.config.Host)
+
+	// create the verifier from the request
+	// if the request is signed, it will have a signature header
+	verifier, err := httpsig.NewVerifier(c.Request)
+	if err == nil {
+		// 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
+		requestingPublicKeyID, err := url.Parse(verifier.KeyId())
+		if err == nil && requestingPublicKeyID != nil {
+			// we managed to parse the url!
+
+			// if the domain is blocked we want to bail as early as possible
+			blockedDomain, err := m.blockedDomain(requestingPublicKeyID.Host)
+			if err != nil {
+				l.Errorf("could not tell if domain %s was blocked or not: %s", requestingPublicKeyID.Host, err)
+				c.AbortWithStatus(http.StatusInternalServerError)
+				return
+			}
+			if blockedDomain {
+				l.Infof("domain %s is blocked", requestingPublicKeyID.Host)
+				c.AbortWithStatus(http.StatusForbidden)
+				return
+			}
+
+			// set the verifier on the context here to save some work further down the line
+			c.Set(string(util.APRequestingPublicKeyVerifier), verifier)
+		}
+	}
+}
+
+func (m *Module) blockedDomain(host string) (bool, error) {
+	b := &gtsmodel.DomainBlock{}
+	err := m.db.GetWhere([]db.Where{{Key: "domain", Value: host, CaseInsensitive: true}}, b)
+	if err == nil {
+		// block exists
+		return true, nil
+	}
+
+	if _, ok := err.(db.ErrNoEntries); ok {
+		// there are no entries so there's no block
+		return false, nil
+	}
+
+	// there's an actual error
+	return false, err
+}