Fix URL related escaping for oauth2 (#37334)

Follow up #37327. See the comments.

* Root problem: the design of OAuth2 providers is a mess, the display
name is used as provider's name and used in the URL directly
* The regressions:
* When trying to fix https://github.com/go-gitea/gitea/issues/36409 , it
introduced inconsistent URL escaping for the "path" part.
* This fix: always use "path escaping" for the path part, add more tests
to cover all escaping cases.

Now, frontend "pathEscape" and "pathEscapeSegments" generate exactly the
same result as backend.

services/context/base_path.go

@@ -44,9 +44,9 @@ func (b *Base) PathParamInt(p string) int {
 
 // SetPathParam set request path params into routes
 func (b *Base) SetPathParam(name, value string) {
-	if strings.HasPrefix(name, ":") {
-		setting.PanicInDevOrTesting("path param should not start with ':'")
-		name = name[1:]
-	}
 	chi.RouteContext(b).URLParams.Add(name, url.PathEscape(value))
 }
+
+func (b *Base) SetPathParamRaw(name, value string) {
+	chi.RouteContext(b).URLParams.Add(name, value)
+}

services/context/context_response.go

@@ -22,6 +22,7 @@ import (
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/structs"
 	"code.gitea.io/gitea/modules/templates"
+	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/modules/web/middleware"
 )
 
@@ -143,11 +144,9 @@ func (ctx *Context) NotFound(logErr error) {
 }
 
 func (ctx *Context) notFoundInternal(logMsg string, logErr error) {
+	// TODO: it's safe to show the error message to end users if the error is fully controlled by our error system
 	if logErr != nil {
 		log.Log(2, log.DEBUG, "%s: %v", logMsg, logErr)
-		if !setting.IsProd {
-			ctx.Data["ErrorMsg"] = logErr
-		}
 	}
 
 	// response simple message if Accept isn't text/html
@@ -166,11 +165,17 @@ func (ctx *Context) notFoundInternal(logMsg string, logErr error) {
 
 	ctx.Data["IsRepo"] = ctx.Repo.Repository != nil
 	ctx.Data["Title"] = "Page Not Found"
+	ctx.Data["ErrorMsg"] = "" // FIXME: the template never renders this message, need to fix in the future (and show safe messages to end users)
 	ctx.HTML(http.StatusNotFound, "status/404")
 }
 
 // ServerError displays a 500 (Internal Server Error) page and prints the given error, if any.
+// If the error is controlled by our error system, a related 404 page can be displayed instead.
 func (ctx *Context) ServerError(logMsg string, logErr error) {
+	if errors.Is(logErr, util.ErrNotExist) {
+		ctx.notFoundInternal(logMsg, logErr)
+		return
+	}
 	ctx.serverErrorInternal(logMsg, logErr)
 }