github.com/google/go-safeweb@v0.0.0-20231219055052-64d8cfc90fbb/safehttp/plugins/csp/strict.go (about)

     1  // Copyright 2022 Google LLC
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //	https://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package csp
    16  
    17  import (
    18  	"strings"
    19  
    20  	"github.com/google/go-safeweb/safehttp"
    21  	"github.com/google/go-safeweb/safehttp/plugins/csp/internalunsafecsp"
    22  )
    23  
    24  // StrictPolicy can be used to build a strict, nonce-based CSP.
    25  //
    26  // See https://csp.withgoogle.com/docs/strict-csp.html for more info.
    27  type StrictPolicy struct {
    28  	// NoStrictDynamic controls whether script-src should contain the 'strict-dynamic'
    29  	// value.
    30  	//
    31  	// See https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/script-src#strict-dynamic
    32  	// for more info.
    33  	NoStrictDynamic bool
    34  	// UnsafeEval controls whether script-src should contain the 'unsafe-eval' value.
    35  	// If enabled, the eval() JavaScript function is allowed.
    36  	UnsafeEval bool
    37  	// BaseURI controls the base-uri directive. If BaseURI is an empty string the
    38  	// directive will be set to 'none'. The base-uri directive restricts the URLs
    39  	// which can be used in a document's <base> element.
    40  	//
    41  	// See https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/base-uri
    42  	// for more info.
    43  	BaseURI string
    44  	// ReportURI controls the report-uri directive. If ReportUri is empty, no report-uri
    45  	// directive will be set.
    46  	ReportURI string
    47  	// Hashes adds a set of hashes to script-src. An example of a hash would be:
    48  	//  sha256-CihokcEcBW4atb/CW/XWsvWwbTjqwQlE9nj9ii5ww5M=
    49  	// which is the SHA256 hash for the script "console.log(1)".
    50  	//
    51  	// For more info, see: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/script-src
    52  	Hashes []string
    53  }
    54  
    55  // Serialize serializes this policy for use in a Content-Security-Policy header
    56  // or in a Content-Security-Policy-Report-Only header. A nonce will be provided
    57  // to Serialize which can be used in 'nonce-{random-nonce}' values in directives.
    58  func (s StrictPolicy) Serialize(nonce string, _ safehttp.InterceptorConfig) string {
    59  	var b strings.Builder
    60  
    61  	// object-src 'none'; script-src 'unsafe-inline' 'nonce-{random}'
    62  	b.WriteString("object-src 'none'; script-src 'unsafe-inline' 'nonce-")
    63  	b.WriteString(nonce)
    64  	b.WriteByte('\'')
    65  
    66  	if !s.NoStrictDynamic {
    67  		b.WriteString(" 'strict-dynamic' https: http:")
    68  	}
    69  
    70  	if s.UnsafeEval {
    71  		b.WriteString(" 'unsafe-eval'")
    72  	}
    73  
    74  	for _, h := range s.Hashes {
    75  		b.WriteString(" '")
    76  		b.WriteString(h)
    77  		b.WriteByte('\'')
    78  	}
    79  
    80  	b.WriteString("; base-uri ")
    81  	if s.BaseURI == "" {
    82  		b.WriteString("'none'")
    83  	} else {
    84  		b.WriteString(s.BaseURI)
    85  	}
    86  
    87  	if s.ReportURI != "" {
    88  		b.WriteString("; report-uri ")
    89  		b.WriteString(s.ReportURI)
    90  	}
    91  
    92  	return b.String()
    93  }
    94  
    95  // Match matches strict policies overrides.
    96  func (StrictPolicy) Match(cfg safehttp.InterceptorConfig) bool {
    97  	_, ok := cfg.(internalunsafecsp.DisableStrict)
    98  	return ok
    99  }
   100  
   101  // Overridden checks the override level.
   102  func (StrictPolicy) Overridden(cfg safehttp.InterceptorConfig) (disabled, reportOnly bool) {
   103  	disable := cfg.(internalunsafecsp.DisableStrict)
   104  	return disable.SkipReports, true
   105  }