Hide sensitive header values in show (#1127)

With this patch the values for the headers `Authorization`,
`Proxy-Authorization`, `Cookie` and `Set-Cookie` are masked with `*`s
when `HTTP.Request`s and `HTTP.Response`s are `show`n. These headers may
contain sensitive information and masking the values reduces the risk of
leaking something.

CHANGELOG.md

@@ -9,6 +9,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 - Server errors are no longer serialized back to the client since this might leak sensitive
   information through the error message. ([#1126])
+- When `show`ing `HTTP.Request` and `HTTP.Response` the values for the headers
+  `Authorization`, `Proxy-Authorization`, `Cookie`, and `Set-Cookie` are masked with `*`s
+  since they might include sensitive information. ([#1127])
 ### Fixed
 - Restrict `HTTP.isredirect` to arguments of integer types. ([#1117])
 - Fix `HTTP.getcookies` error when key doesn't exist. ([#1119])

src/Messages.jl

@@ -609,7 +609,16 @@ function Base.show(io::IO, m::Message)
     end
     println(io, typeof(m), ":")
     println(io, "\"\"\"")
-    writeheaders(io, m)
+
+    # Mask the following (potentially) sensitive headers with "******":
+    # - Authorization
+    # - Proxy-Authorization
+    # - Cookie
+    # - Set-Cookie
+    header_str = sprint(writeheaders, m)
+    header_str = replace(header_str, r"(*CRLF)^((?>(?>Proxy-)?Authorization|(?>Set-)?Cookie): ).+$"mi => s"\1******")
+    write(io, header_str)
+
     summary = bodysummary(m.body)
     validsummary = isvalidstr(summary)
     validsummary && write(io, summary)

test/messages.jl

@@ -197,6 +197,20 @@ using JSON
         # https://github.com/JuliaWeb/HTTP.jl/issues/828
         # don't include empty headers in request when writing
         @test repr(Request("GET", "/", ["Accept" => ""])) == "Request:\n\"\"\"\nGET / HTTP/1.1\r\n\r\n\"\"\""
+
+        # Test that sensitive header values are masked when `show`ing HTTP.Request and HTTP.Response
+        for H in ["Authorization", "Proxy-Authorization", "Cookie", "Set-Cookie"], h in (lowercase(H), H)
+            req = HTTP.Request("GET", "https://xyz.com", [h => "secret", "User-Agent" => "HTTP.jl"])
+            req_str = sprint(show, req)
+            @test !occursin("secret", req_str)
+            @test occursin("$h: ******", req_str)
+            @test occursin("HTTP.jl", req_str)
+            resp = HTTP.Response(200, [h => "secret", "Server" => "HTTP.jl"])
+            resp_str = sprint(show, resp)
+            @test !occursin("secret", resp_str)
+            @test occursin("$h: ******", req_str)
+            @test occursin("HTTP.jl", resp_str)
+        end
     end
 
     @testset "queryparams" begin