backport of commit 6ae4399 (hashicorp#19790)

Co-authored-by: Violet Hynes <violet.hynes@hashicorp.com>

vault/request_handling.go

@@ -2199,8 +2199,32 @@ func (c *Core) PopulateTokenEntry(ctx context.Context, req *logical.Request) err
 	token := req.ClientToken
 	var err error
 	req.InboundSSCToken = token
+	decodedToken := token
 	if IsSSCToken(token) {
-		token, err = c.CheckSSCToken(ctx, token, c.isLoginRequest(ctx, req), c.perfStandby)
+		// If ForwardToActive is set to ForwardSSCTokenToActive, we ignore
+		// whether the endpoint is a login request, as since we have the token
+		// forwarded to us, we should treat it as an unauthenticated endpoint
+		// and ensure the token is populated too regardless.
+		// Notably, this is important for some endpoints, such as endpoints
+		// such as sys/ui/mounts/internal, which is unauthenticated but a token
+		// may be provided to be used.
+		// Without the check to see if
+		// c.ForwardToActive() == ForwardSSCTokenToActive unauthenticated
+		// requests that do not use a token but were provided one anyway
+		// could fail with a 412.
+		// We only follow this behaviour if we're a perf standby, as
+		// this behaviour only makes sense in that case as only they
+		// could be missing the token population.
+		// Without ForwardToActive being set to ForwardSSCTokenToActive,
+		// behaviours that rely on this functionality also wouldn't make
+		// much sense, as they would fail with 412 required index not present
+		// as perf standbys aren't guaranteed to have the WAL state
+		// for new tokens.
+		unauth := c.isLoginRequest(ctx, req)
+		if c.ForwardToActive() == ForwardSSCTokenToActive && c.perfStandby {
+			unauth = false
+		}
+		decodedToken, err = c.CheckSSCToken(ctx, token, unauth, c.perfStandby)
 		// If we receive an error from CheckSSCToken, we can assume the token is bad somehow, and the client
 		// should receive a 403 bad token error like they do for all other invalid tokens, unless the error
 		// specifies that we should forward the request or retry the request.
@@ -2211,9 +2235,16 @@ func (c *Core) PopulateTokenEntry(ctx context.Context, req *logical.Request) err
 			return logical.ErrPermissionDenied
 		}
 	}
-	req.ClientToken = token
+	req.ClientToken = decodedToken
+	// We ignore the token returned from CheckSSCToken here as Lookup also
+	// decodes the SSCT, and it may need the original SSCT to check state.
 	te, err := c.LookupToken(ctx, token)
 	if err != nil {
+		// If we're missing required state, return that error
+		// as-is to the client
+		if errors.Is(err, logical.ErrPerfStandbyPleaseForward) || errors.Is(err, logical.ErrMissingRequiredState) {
+			return err
+		}
 		// If we have two dots but the second char is a dot it's a vault
 		// token of the form s.SOMETHING.nsid, not a JWT
 		if !IsJWT(token) {